Invest in a good roller
Dry Your Brush
If you are going to reuse a brush that has just been cleaned with water, blow it dry with a hair dryer first. Any residual water in the bristles will dilute the paint on the brush, causing it to run down the handle when painting. If the brush has just been cleaned with mineral spirits, dry the bristles as well as possible with paper towels before starting to paint. Spread the paper towel out to dry before disposing.
Getting A Cleaner Edge
If using masking tape to protect a surface (except carpet) when painting, remove the tape as soon as you can. You will get a cleaner "edge" and there is less chance the tape will bond to the surface it is protecting and become difficult to remove. Masking tape comes in many grades and qualities so talk to your paint supplier to make sure you get the right tape for the job you are doing.
Resealing The Can
After opening, and before using a new can of paint, drive about 5 or 6 holes with a nail around the rim where the lid sits. This will allow paint to drain back into the container instead of filling the rim. If the rim fills with paint, it is difficult to reseal the can.
Invest In A Good Brush
Buy a good-quality brush or roller. A cheap brush loses bristles, doesn't hold as much paint, and is harder to use when "cutting in" to another surface. Cheap rollers tend to matt and leave an uneven "stipple" on the surface.
Keep A Wet Edge
When brushing or rolling, always work from the dry surface back into the wet paint, working fast enough to keep a wet edge. If you are going to take a break, do it in a corner, never in the middle of a wall. This will help avoid lap and roller marks in the painted surface.
Use An Extension Pole
Use an extension pole on your roller handle. It allows you to use longer strokes and saves you from bending over to refill the roller with more paint. It also speeds up the job and makes it easier to maintain a wet edge — especially on a ceiling.