this has been mentioned in many background tutorials, but I figure it couldn't hurt to spread a bit of friendly advice since a lot of my watchers watched me for my pixel BGs!
a friend pointed this out to me a while ago and my BGs have improved by about 200% since i got more serious about watching my values and contrast
like, look at these old BGs. they look okay, except they're about 90% comprised of "the mid-tones of meh". the dark areas are not very dark, and the light areas that should be standing out are getting lost.
then compare these BGs:
wow, much contrast, so drama! the areas of light and dark are well-defined. aspects of the pie