My personal painting tip is "Don't!"
I've been painting several rooms in my house over the last few months. I'm not sure how to best describe my experience, but the colors I chose for the walls turned out to be a tinge darker, but they were also more vibrant than they appeared on the sample pieces.
I bought quarts of the colors I thought would look good and painted a good sized sample on the walls. One color was fine, but the other one wasn't, so I had to look for something else. The problem, for me, wasn't so much that the color looked so much different on the wall than on the sample, but, rather, a much larger amount of that particular color wound up not looking good as a background for some fabric I'd chosen to use for window coverings. When I was using the small paint sample, it looked wonderful. I'd strongly recommend testing with quarts; yes, it's more expensive, but it isn't as much more expensive than buying a gallon and learning within three brushloads that the color is wrong.
As I moved through the projects, I wound up buying three different brands of paint. One was Valspar by Lowe's and called interior satin, one off brand that I think is actually a Dutch Boy paint is called eggshell finish, and the third (a Northwest brand) was called satin enamel. They're all a touch harder finish than straight flat wall paint, but they have no gloss and are washable.
Interestingly, the one that was actually the easiest to use and really did cover in one coat was the store brand called "HD Design" that I bought at Fred Meyer, and it was only $14.99 a gallon compared to the $25 per gallon (plus or minus) that I paid for the name brands. It turned out to be my favorite of the three to work with. Go figure.
I strongly recommend the quart sized sample, even if you do gag on the price. It turned out to be worth it when I was choosing specific colors.
Edit: I suppose I should have added that the Valspar from Lowe's was fine, too. It didn't cover in one coat, but the color I chose was also quite dark in comparison to what was being covered.