Just like everyone else said - practice, and observe the world around you.
Right now I am trying to make my materials better as well. Every day I look at how materials reflect light, where that light bounces to, the texture (LITERALLY TOUCH THE MATERIAL), the refraction if any. Go out and take pictures, even a cell phone works for this. Pick a material, lets say concrete, and go out and take pictures of different types of concrete at different angles. You'd be surprised at how reflective a material is at a sharp angle. Almost like glass in some cases.
I've also read on various CG Forums that you should exaggerate your materials. Make the color just a bit more saturated, make the reflectivity just a bit more reflective. Also don't forget that everything has fresnel. Everything has reflectivity - or else you wouldn't be able to see the object.
Never use 100% black or white (use 180, 180, 180 for white).