After the compound has completely dried sand down any ridges that resulted from the putty knife.

This step will be messy! Everything in the room will get some dust on it, so either use dropcloths or be ready to clean when you're done.

Also, be careful not to get dust in your eyes, or inhale dust. You may wish to wear goggles and a dust mask.

Don’t sand into the tape.

You still want the compound to cover the tape and its contours completely.