GvG at a glance
Although most do not care about their rating, GvG is not about profits or breaking crystal. Essentially it is about bragging rights. Who can work as a team the best to overcome the other guild. Yes, it can be quite profitable at times, but unfortunately this is because most guilds are not set up to protect themselves adequately, and Im seeking to change that.
Offline sets
At most levels, an attack/damage suicide set is the ideal offline set. You see, any set can be beat without buffs rather easily. The plan here is to setup your sets to be optimum with buffs, and pay attention for incoming attacks. Remember GVG is a team effort, if you plan on going to the top, you will need to help one another buy buffing/buying buffs for one another while being attacked. Coverage is the most important factor, not sets. Anyways, back to the sets. A suicide set is normally attack heavy. Its best to have the most attack with KE, while maintaining enough damage that a piercing strike will kill the max sum of armor possible in whatever level range. Armor and defense are generally unimportant.
Wait, what? Armor and defense unimportant when Im defending???
Yes, the idea is to make it impossible for your opponent to be safe in an attack against you should you get a hit in. There are 5 ways to gain a strike while defending without armor or defense. These are: Dodge, First strike, Force shield, Last Ditch, and the 2% miss. As I said, any set is easily beatable without buffs, so you are setting up to have Force shield and last ditch, as the combination of both creates frequent chances to hit back whist defending.
Why is attack more important then damage?
Well, effective ways to kill armor include Piercing strike, critical hit, Shield strike, Shatter armor, Reflection, and if your setup has armor, savagery. Shield strike alone is is 17.5%, and makes use of armor vs a proper set highly unreliable
On the other hand, if your opponent manages to beat your attack with defense, all you have to rely on is the 2% random hit rule. Although between the 5 saves I mentioned earlier, these are fairly common, buffs like SW and stun will greatly reduce the odds of such, and buffs like LD and FS will sometimes save vs that 2%.
Level ranges where a suicide set is not viable/you cannot afford the set that will stop the max defense sets-
That is when you want to add an armor or defense second stat. My preference has always been defense, since most max defense sets attacking you tend to have very little attack, adding a bit of defense to a suicide set can sometimes stop a set from gaining the right balance to beat you. This, and if all else fails, there is savagery which will randomly add your defense into you attack stat, creating a very bad situation for the attacker should you save
Armor can sometime be good as a second stat as well. Even if all else fails and you do not have sufficient attack to hit your attacker, if they are not using sufficient damage to one hit you, or at least not one hit you when reinforced armor or nullify go off, then you are increasing the the chance at the 2% hit greatly with every swing you take.Offense
No war has ever been won by defensive action alone. Attacking in GVG is an intricate process. Remember its a team effort, do not try to be a hero. If your target(s) are buffed, check to see if any of your guildmates have viable targets unbuffed and such for them to chime in. You have to remember, even without buffs, there is always a chance for that 2% miss, and most targets have the enhancements first strike and dodge you have to worry about as well.
Safest way to attack- If your target has no buffs, if you can get out of range of your targets piercing strike damage stat with armor, this really is about the safest way. Once they are buffed though, armor can quickly become the most unreliable method as stated above under "offline sets". Remember much like hunting you have to maintain the attack to hit your opponent, and the damage to kill their armor+HP added together in order to kill them in one hit(its normally best to have more then 25% more then their armor+hp added together in order to override reinforced armor or nullify) The next safest way I know of is often difficult to obtain, known as the "turtle method" or simply "turtleing". The turtle method is to cover your targets attack with defense, and also cover their damage with armor, making it so the only way they kill you is a mixture of the 2% hit and a armor killer such as piercing strike, which do not line up often. This is often hard to do, but alot of max defense sets often leave very little damage or attack, so its possible to get them within range(especially using DC225, which is a 45% reduction in defense) you can tweak a max attack setup to have enough defense and armor to cover both your target's offensive stats. Remember the buff fortitude will be a great help here, as you gain HP for the amount of defense you have. The next most reliable is of course defense. You really only have to worry about the 2%, and buffs like SW and Stun will reduce this alot when your target has save buffs like LD and FS.
Buffs
A few important notes on buffs-
LD and FS- If all else fails LD and FS are huge helps and increase the odds of the 2% or piercing strike or whatnot, and therefore are like the most important buffs to have on your players that are being hit. Also very important to have while attacking, because you never know when a battle will randomly go against you(I.E. your target being buffed inbetween the time you view their profile and the time you attack)
Reflection- The ultimate armor killer. Or is it? Reflection adds damage dealt to your next combat strike, not your damage stat. What this means is if you hit your opponent for 100 damage and they have reflection 175 and activate last ditch(Note that reflection doesnt work well with force shield as the damage dealt was reduced to one) they will hit you back for 17 damage extra then they would regardless of your armor stat(17.5% of 100 is 17.5, )
So the trick to getting around reflection is to increase your HP, and lower your damage to it being barley lethal, but not enough that 17.5% of you damage dealt will be enough to kill your HP. You are still at risk if you critical hit, piercing strike(vs certain sets) or if your opponent kicks in with wither and/or bloodthrist(if you have insufficient HP to handle these)
Absorb- If your guildmates set has any armor, or you notice the person attacking them is using low damage, absorb can be as effective as LD or force shield. Note that it will also be counter productive when your guildie is using reflection though
EW 1500- Spare no expense! Your guilds honer and pride are at stake here, and this is one of the best pvp buffs while attacking. Many of the suicide sets I mentioned above, the only way to beat them when they are buffed with defense is using a high defense weapon and ew1500(along with many other buffs)
Random notes/advanced strategy
Gear level-
If you pvp often, its best to leave room in levels for you gear should someone decide to take 5 levels from you. If you lose your levels under the min level of your gear, the stats from that gear disappear leaving you at a huge disadvantage. On the same note, if you see someone near their gears level in a rival guild, take levels from them if you can prior to a gvg. There is no dishonor in it. Its battle. Battles are about exploiting weakness, and not planning ahead like that is a weakness.
Relics-
Relics are nasty little weapons when used right. If you care enough about GVG, even if you know you cant hold them, they are worth empowering for the 1 hour you get to hold them no matter what if needed. If your attacked by a guild with holding a relic, try to take it if you can. Or if your guildmate doesnt have the attack to hit the attacker, go find an attack relic, grab it and empower it, most guilds dont check to see these things whilst doing incoming. They are a powerful tool on either offense or defense in GVG.
Blitz-
You attacking another guild that cares about GVG and are well setup? Most are the top gvg guilds are small, do what you can to wait until all their members are offline(some guilds even with few members this is rare), and go in with teammates to complete it as fast as possible. Speed and momentum are deciding factors in historical battles, and no different in gvg. As I said before, coverage is key. There is no dishonor in attacking a guild with no green lights are on, they simply let their guard down, and after all, it is the biggest weakness small guilds have in gvg.
Misdirection-
Have someone who isnt partaking in the conflict initiate it. Either that or the person who has the least amount of targets. Preferably someone who can sit in a setup that looks like they are attack and have buffs running. These makes it take more time for the defenders to figure out who is attacking, and will be slower to buff the targets of who is actually participating in the conflict, not to mention watching the defenders waste stamina buffing people who are not being hit
Quick Recap on most important notes.
1-Have all members in attack sets that are optimum when buffed.
2 Always have a sufficient save stat while attacking.
3 COVERAGE! Its a team event! Watch your conflict page for incoming. If you use tabbed browsing, have a tab just for it.
Credentials
Just in case you see I wrote this while not in a guild, or if your reading this in the future and you notice whatever guild I may be in isnt a gvg guild and/or has a losing record or whatnot, I was a charter member of the guild Epic, and later the founder. We stayed top ten-15 for many months, the latter few being mostly in the top 5, and even obtained first place for a short period of time. It was not because of me alone, but a very strong team effort by all members.
(Guide accurate as of original posting date. Note that gvg evolves as sets/rules/HCS change and or implement things, and this is to fit the current situation, as is)
Highlights from the rest of the thread
If you are too lazy to read the whole thing, this is what others have helped contribute I felt important. (Note, Im biased of course and reading the whole thing would be most benificial should gvg be an interest of yours)
The worst problem there is letting their members go offline gearless(I mean nothing can really save you if you don't wear anything)
Remind guild founders to strip a person of their equipment only after 7 days, when they cant be viable targets.
I should likely fix the spelling and capitalization on this one, but I would rather quote it as they say it so it doesnt look like Im changing things-
Target finding
when your guild is under attack you need to find the attacker and buffs the targets as soon as you can. once an attack starts i go to the page of and go threw a process of elimination. first i go down the list and open in a new tab anyone with a green dot. then i see who has been away for 10+ mins and close those tabs (for now at least). then i check items they have. if i see a level 750 in a gurg set and oggy gloves i can bet they arent attacking and close those tabs. then i check buffs. the players with anything PvP useful are more than likely the culprits. by this time ive found the attacker or only have a few possible people it could be (could always be more than one). if im still not sure i hit refresh on the guild conflict page and refresh on the tab. if i see 4 attacks got made and one online players stam dropped by 40 or two online players drop by 2 i know exactly who to buff and to tell other to buff. also buff everyone in there attack range not just the players they are attacking.
Alot of attack items are actually really cheap because they tend to be "low interest"/ And they dont need to be F/F or anything. As for the buffs, people under estimate low level buffs. I know my level 145s won alot of conflicts for us that I was surprised at, and all it takes is having a few pvp buffers online willing to contribute to the guilds greater good 
) not all.Overall the main idea is that if you plan to GvG you need people to help you with buffs,simple as that...to keep an eye on you and your gear.
a link to this would save me a lot of typing when trying to explain to potential new members about offline gear 
Another thing worth noting is that crystal items dont lose their stats until completely smashed like other items do, making them that much more effect.