Sandpaper is used to remove small quantities of material at a time from the surface of an object. Sandpaper can be used to remove a specific material from an object (such as a layer of paint) or to level and/or smooth the surface of the object. Sandpaper comes in many numbered "grades," with smaller numbers being coarser and removing more surface material with each pass. Higher numbers are finer and remove less material with each pass of the paper. Sandpaper can be used wet to eliminate dust or dry and can be used by hand or wrapped around a sanding block to make sanding large, flat areas easier. However you use your sandpaper, there are a few simple rules for getting the best finish possible.
Decide how much surface material must be removed. If surface is rough or dented or if a layer of paint must be removed, choose the coarser grit of sandpaper (60-grit). If the surface is almost smooth already, choose the 100-grit paper. Wear a breathing mask and eye goggles whenever sanding.
Hold the sandpaper against the object with the tips of your fingers or wrap the paper around a sanding block according to the block manufacturer's directions. Begin moving the sandpaper back and forth over the surface of the object, sanding with the grain if sanding wood or sanding in one direction if sanding paint. Use moderate pressure and continue sanding until the surface is almost smooth and level.
Set the 60-grit sandpaper aside and continue sanding in the same manner with the 100-grit sandpaper. Sand until the surface feels smooth to your fingertips. Set aside the 100-grit paper.
Sand in the same manner using the 120-grit sandpaper, but using a light touch. Sand only until the surface feels as smooth as glass.
Wipe the surface with your tack cloth and inspect it carefully for any imperfections. Small imperfections can be fixed using the 120-grit paper; larger imperfections may require the use of the 100-grit paper followed by the 120-grit paper. When you are finished the surface of your object should look and feel almost as smooth as glass.