Take the time to do it right and you will not be sorry about the end results, here is some tips to getting started.
Surface flaws - Use plaster to cover any small holes and cracks, if your in a hurry try a little bit of durabond 90, its a little harder to sand but your ready to paint over it in about 90 minutes.
Use Quality tools - Cheap rollers and brushes at the dollar store don't cut it for a decent job, shell out a few extra dollars for the good brushes and rollers.
Wipe down the walls with TSP - Trisodium Phosphate is a great chemical for opening the pores of a wall and really allowing the new paint to stick, I highly recommend using it.
Paintable caulking is also a great way to fill some minor holes or to smooth out some surfaces before painting.
Orange Peel - If you want to avoid the bumpy look, simply sand a bit between coats. Use some fine grit paper like 120 and give the wall a quick sand, the end results and a nice smooth wall will result.