The tools and materials used for patching a wall are very important in terms of ease of use and satisfactory results.
Choose a good six or four inch putty knife. A good putty knife will have a medium flexibility, it should flex slightly when pressed against a wall.
As a rule most patching compounds that dry quickly are difficult to sand. I recommend standard wallboard ( taping ) joint compound for patching wallboard (drywall) or plaster.
A mudd tray or a clean flat board with a straight edge will also be needed.
Patch dings, gouges and dents by scooping a small amount of compound onto the putty knife. Place the knife on the wall at about 45 degrees and about 4 or 5 inches from the damaged area. Pull the knife across the damaged area with a steady pressure. Scrape the excess compound off the knife by pulling it across the edge of a board or mudd tray. Make two more passes across the area, removing the excess from the knife after each pass. Let the patch dry.
Because of compound shrinkage the patch may require one more application as above.
Make a simple sanding block by wrapping a piece of 120 grit sand paper around a hand size wooden block. Sand the patch from the outside edges inward. Be sure to feather the edges into the surrounding area, rub your hand across the patch to feel for hard edges. Paint will not hide the un-sanded hard edges of a patch.
Prime the area with the wall paint before you paint the entire wall.
Holes require a backing material. For small holes use standard 2 inch ( wide) drywall taping mesh available at hardware and supply stores. Cut a length of mesh to extend a few inches on either side of the hole, apply sticky side to the wall and over the hole, smooth out the mesh with the putty knife.
Apply wallboard compound over the mesh with even pressure. Allow to dry. Sand lightly and apply a second coat of compound , allow to dry. Feather sand and prime the patch with wall paint before painting the entire wall.