1. Rain, rain go away!  High humidity will slow down drying time and multiply dripping. So if it is a hot humid day or simply rainy, consider painting another day.  
2. A job is only as good as the prep. Look for cracked or peeling paint to sand or scrape.  Then prime the walls before painting to ensure a quality paint job. 
3. Select the proper tools. Don’t skimp on paint brushes or rollers.  Be sure to buy the right tools for the job, such as the proper nap on your rollers. 
4. Box your Paint. If your job requires multiple gallons, dump them all into a large container, then mix throughly. 
5. Cut in first. Then roll the wall color from top to bottom. Keep your pressure on your roller even to get a consistent finish. 

Now get painting…nothing transforms a room more quickly.