Here are a few tips that should help you out if you want to tackle that project by yourself. Remember, we're here if you get into trouble or if you just don't want to deal with the hassle, but if you want to have a go at it yourself, read on:
Sand, Sand, and Sand Some More!
Any surface you are going to paint on has to be flat. It literally cannot be flat enough. The slightest ripple or texture can cause an annoying seam that will nag at you for years to come. When you think you've sanded enough, sand it once more. Seriously. Then completely inspect it, making sure to remove all dust, apply a coat, wait and inspect before proceeding.
Cleanliness is Next to Godliness
A dirty work area is never a good thing unless you are a pig farmer. When it comes to painting, a clean, organized work area is mandatory. Spilled drinks or smudges can destroy all your hard work, loose garbage can blow into a wall, and the last thing that you want is to get moisture or dirt between the wall and the paint you just spent all of that time sanding.
Buy More Than You Need
While we have a formula for painting a room, we do this professionally and we keep large stocks, paint color mixtures on record, and distributors that can make almost any paint. As you are doing this yourself and don't likely do it too often, buy enough to allow for mistakes, and to allow for touch ups down the road. A new coat of paint can peel or chip, and you might not find that mixture you chose at a later date if the hardware store doesn't carry or make it anymore.