honestly, i mostly just messed with gradients in a lot of places LOL i like how they look and i think it makes my page look less plain! idk what other types of gradients you can use but i mainly use linear and radial!
you can use images in more spots than just the background i believe (i dont think it works on text color or shadows though), but i just use colors on everything besides the background
i also colorpicked directly from my graphics (specifically my icon) to make sure it would match! im personally very particular about that sort of stuff LOL

if you have any more questions about it please ask! i don't mind answering at all :D