Sometimes you can conceal a flaw, whether it is a dent or poorly executed drywall, by repainting without having to mess with drywall, sanding and priming. Textured paints are an excellent way to conceal flaws, as are dark paints. The latter reflect less light, thereby concealing minor flaws. Faux painting is also useful, as flaws can be disguised in a pattern. Sponging is one method of patterning where you use a sponge or wadded cloth to dab a lighter color over a darker one.
The finish of your paint makes a big difference in just how visible minor imperfections are. Glossy or satin finishes are much less forgiving, due to the amount of light they reflect. This actually has the opposite effect of highlighting and bringing out those flaws. Go with a flat finish to effectively disguise flawed walls.
Textured wallpaper is another effective way of covering up those flawed walls. The texture in the paper distracts and camouflages bumpy or wavy drywall. Any wallpaper, whether it is textured or not, is good at concealing scratches, marks and gouges.
A quick fix for hiding imperfections is just that --- hiding them. Depending on where on the wall the problem lies, you can use all manner of items to hide it. Strategically place a piece of furniture or a plant in front of the problem. Hang a picture or a mirror over the area to conceal flaws higher up on the wall. Any number of these decorating techniques can take your wall's blemish out of the spotlight and place it on the back burner.