there are two things that you have to take note of - the fact that most lcd monitors are not going to give you a full dynamic range possible.
the dpreview site always has a bottom bar that gives you black to shades of grey to white. optimally you should be able to see all the graduations. every little bar in there should be a different shade on your screen, and not burnt out, or become one block of black.
for color.. the only way (that i know of) to make sure you're doing it right is to print your stuff at a good lab and compare.