Turntables...I just take the thing apart (not the actual mechanism that runs it, just the easy to take off things), clean everything, make sure there isn't half of a record stuck in some crack. Then, before finishing the turntables, I go onto the mixer.
Once again, I make sure everythings clean. Then, I tweak all the knobs, slides, etc to make sure everything moving smoothlty, then I play something through it at max volume (well, as high as I can and not damage anything

). While doing this I basically give the thing a good work out and listen closely for cracks, distortion, pops, and make sure everything checks out.
I usually do all of this before every set I do.