Preparation is the number 1 thing to get a great long lasting paint job.
Ensure that the surface you are painting onto is clean of dust and grease.
Paint doors and windows early in the day so you will be able to close them at the end of the day.
If you wear glasses when you paint, cover the lenses with cling wrap, when finished just remove the wrap.
Always remove door and window fittings before you paint. If previously painted scrape old paint out of screw slots before trying to unscrew them.
If painting on extremely hot day using water based paints, try putting a light mist coat of water on the surface prior to painting. It will help the paint flow and not dry to fast. (Don't over wet the surface)
Remove masking tape before paint is completely dry and hard. This way it will help to stop you from tearing or chipping your fresh paintwork