Assume that the walls are smooth to your satisfaction, i.e. you have taped and sanded the seams, filled in the screw holes, etc.
1 box of drywall mud
8 inch drywall knife
Step 1: Water down the Mud
Rather than use a heavy mixer bit and drill, I just used a wire whisk from the kitchen.
Step 2: Trowel it on
When you're done, the section of wall you just did should look peaked like a cupcake.
After a few moments of drying time, the thicker mud, closer to the wall, will be dry, while the thinner high peaks will still be wet.