I started flipping bikes last year after I was schooled by two of the best (Bigbossman and mswantak)
Anyways here's what do. First I never like mismatched parts so Suntour with suntour etc. and if I need stuff I go find it at swap meets, trade with the guys I know on the bbs, and hit this one LBS that keeps old parts around. I buy stuff in bulk tires, cables, tubes, to cut costs. Anyways, for the bike they get new cables, housings, tires and tubes if they need it, wheels trued if needed, new chain if stretched, new bearings in the hubs, new bar tape if it needs it, bottom bracket and headset work if needed. Everything else is cleaned, adjusted, detailed, lubed, wash and waxed. Yeah, it seems like a lot of work and yeah, to be honest I really only make a few bucks here and there but it pays for my bike gear and my ride fees and best of all I get some real enjoyment out of what I do.