Here are some tips for all the graphics makers around here. Keep these in mind and you'll be a pro in no time!
Try different backgrounds, never simply add a texture into a black background as it looks plain.
Use render effects, for example duplicate render 6 times. Layer 1 = Gaussian blur 3 px, layer 2 = Normal at 50-70%, layer 3 desaturated(60%) with full opacity, layer 4 at soft light with 60% opacity, layer 5 at hard light with 20% opacity. Play around with the last 2 layers, they will make or break the sig. For bright sigs, use screen/lighten and for dark ones use multiply but with very low opacity.
Use c4d effect renders behind the render and do Image->Apply Image, then set it to a clipping mask by placing the layer over the c4d, pressing alt and clicking between the two layers. Lower the opacity for nice result. Choose a render with colors that will suit your background.
Never underestimate the power of the smudge tool. Some brilliant backgrounds can be made using the smudge tool. Hell, not only backgrounds but also some great effects - shattered, cloudy, bubbly, liquified, you name it. The smudge tool is very effective in sigs that have a render and not a full stock photo.
About the text, well, here's the deal. It is the kind of thing that can make or break any art work and use it right to create stunning sigs. Try adding a clipping mask onto the text with a full applied image, also try doing adding some layer styles. Sometimes a simple gradient overlay will not do. You need to add stroke, drop shadow, satin, inner shadow and stuff, depending on the nature of your sig.
The last part of the sig will be enhancing the look of it. Do a simple apply image, then duplicate and do a high pass filter, set it to soft light(play around with the opacity). Then again do an apply image, duplicate, then Filter->Sharpen->Sharpen. Erase parts that look bad. Now wherever you have added a light source, keep that in mind and and use the dodge and burn tool to create superb effects, bringing out the focal on your sig. Good luck, always keep these things in mind!