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:
Any surface you are going to paint on has got to be prepared properly. The slightest ripple or texture can cause an annoying seam that you’ll see for years to come. When you think you've completed the prep of patching holes and caulking baseboards and windows, completely inspect it, make sure all dust is removed, apply a primer coat, wait and inspect before proceeding.
A dirty work area is never a good thing. When it comes to painting, a clean, organized work area is mandatory. Spilled drinks or smudges can destroy all of 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 getting ready.
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.
And it can save you from making annoying, time consuming, and even costly mistakes. Tape all corners and seams, sills, anything where you want a crisp even line, that way when your brush goes out of bounds, you don't get a smudge, when you remove the tape, your line will be perfect. Be careful when removing that tape too. And use a tarp over the entire room. You'd be amazed how paint can travel away from where you are working.