Chalkboard Wall

First you must prepare the wall, so that it is flat. My wall had a fairly large hole that I had to plug and finish over first. There should be no holes and it should be flat and dry. Then put your painter's tape up.
Mix paint. The general about is 1 T unsanded grout per about 1/2 cup of any acrylic paint color. Keep in mind that you can make the chalkboard any color you like, but the color of the grout and paint mixing together will determine it's color. Then paint wall. I did two layers. It is very sticky and spiky. Let dry.
At this point you are supposed to sand the surface to make it flat. I did not have a sander, and it was a large surface, so I skipped sanding it. this seems to have resulted in a more prickly wall that I can't use a chalkboard eraser on, but that is fine with me.
Prime the wall by completely covering it in chalk. Let it sit for an hour or so and then wash it off with water. This makes it so that you won't stain the paint with the first design you draw on it. Find sidewalk chalk for this. I originally used tiny chalk and just about took off my fingers. Using a bigger piece of chalk was infinitely better.
If you haven't already done so, pull off painter's tape and enjoy! I use a sponge and a bucket of water to clean off old designs, but if sanded you can use an eraser, or anything else you like.