Painting walls is tedious and tiresome, but there's a simple solution to speed things up. According to Instructables contributor The Family Handyman, you can make it easier for yourself by starting the paint job from a specific side.
Painting the wall from left to right is better and easier for a right handed person. Paint the opposite way if you're a lefty.
The trick is to start on whichever side is oppositive to your dominant hand, roll your paint roller up and down once, then move three inches over and repeat until the wall is done. This should increase the speed of painting, because it gives your dominant hand an advantage.
The Fastest Way to Paint a Wall [Instructables]