Nice to see you getting started with signatures. I think it's easier to learn concepts with a bigger canvas size that you get when making signatures.
First off though, I wanna say when picking out a render or stock image, you should try to find one which already has a well established color scheme/color harmony. I don't expect you to already know what color harmonies are, so I'll link you to a site which demonstrates them for you:
http://kuler.adobe.c...eate/fromacolor. To start off, you probably only want to look at 'complimentary' themes, as the others are harder to incorporate.
The next thing I want to mention is flow, this tutorial/guide briefly demonstrates what a flow is:
http://img507.images.../flowtutzo0.png. This one better demonstrates what a flow and other various aspects of tags that you want to incorporate are:
http://fc01.devianta...TheInterest.png.
Looking specifically at your tag, it looks like your primary flow is going from the upper right-hand corner, to the lower left-hand corner, which is a common flow scheme. You've just got a few c4ds or brushes which contradict that; which isn't always bad if you plan it out right, but they really start to kill your flow.
The next thing I want to point out are colors, some of the 'red' looks too strong, as if it just slaps you on the face. As I mentioned earlier, you should try to use an intial render or stock image which already has a good multicolor color scheme, it'll make your life easier when constructing a color table for colors you want to add into your sig. Once you have your render, look specifically for c4ds/fractals/stock images which compliment upon those colors, and make use of those (you also want them to complement with your flow, remember you can always remove 'bad parts' with respect to your tag using a soft eraser brush
hardness = 0>).
While lighting is probably the next thing I'd touch upon in a critique here, I'd like to say it's well worth your time to focus on the other points I brought up before getting to lighting in tags. So I'll end the critique by saying you can add a decent amount of depth to your focal in a tag by applying the image to a layer before adding your text layer and sharpening it, then erasing over everything but your focal; then following that up with another applied image where you do a soft Gaussian or lens blur (radius < 1px) and erase over your focal.
All in all, this is a great tag for your current skill level with PhotoShop, and I'm looking forward to seeing any improvements or new tags you create upon reading this,
Xel. ^^