Henry is right. Don't skimp on the paint. My personal favorite is Finneren & Haley. (I don't know if it's available in your area.) Painting is the EASIEST part of the job so get some good stuff. It's the PREP work that's a pain. You know, moving furniture, getting rid of 'junk' that's been hiding behind the couch for years, covering things, vacuming. Yea, you do all this stuff and it will make painting look like a picnic! Of course, doing a good 'cut' job and spreading job are crucial too.
I usually put on 2 thin coats. I'm not that good to do the job with one coat. Oh, about that one more thing ... If you're putting a light paint over a dark one, you may want to consider priming first. Otherwise, you run the risk of the dark paint 'bleeding through' to the surface. In other words, your white won't look like white; it may look beige or bone in color if you know what I mean. I know from experience that white over pink w/o priming will cause the pink to bleed through! If you're not certain, prime. Only one coat is necessary.