Sue brings up a good point. Be sure to 'wash' the walls when you're finished. One way to inspect your work is to check it at night or after you make the room real dark. Then, get a flashlight or small wall lamp (that's plugged in), and shine/hold the light right up against the wall. If there is any residue, you'll see small shadows. THAT should help show how well of a job you did.
I assume you're painting. Take a sanding block and 'rough up' the walls just a tiny bit, 220 grit. DON'T press - You only want to 'remove' any residue, and you want to lightly scratch the wall. Then, take a GOOD, QUALITY PRIMER and prime the walls with a 3/8" knap roller. From there, you're on your own!