The single most important factor in painting is preparation.

Fill a mop bucket with water and put a hand towel in it. If you get paint on your hands you can wash them in the bucket. If you make a mistake and get paint on the wrong thing you can stop and erase it immediately with towel.

If you have to stop painting for a while, you don't want the brush to dry out. If you don't want to clean it now you can put it in plastic wrap. Slip the brush into a bottom corner of the bag, than sort of roll it up in the bag. The objective is to wrap it tightly enough no air can get to the paint. This can help you for several hours.

You can put your brushes in to the fridge if you don't want to clean them. Some people say that freezing brushes with latex paint will make a gooey mess. Oil paints must be put in freezer even if it's just a day. When you're starting to paint again, put bag and brush in hot water jar to warm it up before starting to paint again.
When buying paint, keep in mind that dealers have regular sales. Professionals argue that the quality of interior paint isn't very important because it doesn't take much abuse.

Choosing an exterior paint you should pick the best paint. If you do two coats, make the first coat a white primer such as Zinsser Bulls Eye 1-2-3. It hides and holds-up better and longer than two finish coats.

You have to add a topcoat of paint because you cannot leave the primer exposed to weather. If the base is bare wood make it a primer two finish coats. The second finish coat will make a big difference in endurance.