From time to time you are more than likely going to ding your wallpaper or have a seam curl up. Here are a few easy ways to make those repairs.

I have never had much luck with those so called "seam sealers" most stores sell. They are thin and runny and lack good bonding.
Buy a small container of ready mixed heavy duty adhesive, or vinyl to vinyl adhesive which is used to hang borders.
Spread a small amount out on some newspaper and allow the paper to soak up the excess water. This creates a thick very sticky adhesive. Normally an hour or so does the trick. (Save the leftovers when you are thru with your repairs in a small jar and you will have it for future repairs.)

Wallpaper becomes brittle after drying so it is necessary to soften it before trying to paste it back down. Most times a soaking with warm water on a sponge works, if not you can use a hair dryer.

Once it is softened carefully lift the edge and using a butter knife or thin putty knife, spread a little of your thickened paste on the back side of the paper and the wall. Press the paper in place, gently, you don't want to stretch it. Smooth it gently with a spatcula or other flat smoother, clean off excess paste and it's fixed.

Air Bubbles Most bubbles and blisters are just air pockets, but it may be a small bump on the wall or a small piece of debris that was overlooked when the paper was hung. Press on the area and if you feel a speck of something cut an X through the paper, peel the flaps back,remove the debris ,then, apply a small amount of adhesive on the wall area and roll the paper flat.

If the bubble is in fact just air, you can fix the problem with a glue-injecting syringe which is available at most paint stores and home centers like Home Depot and Lowes. Fill the syringe with some thinned down ready mixed adhesive, cut a straight small slit with a razor knife (this way you won't stretch the wallcovering) and squirt in the adhesive. Use your seam roller to flatten the repair and wipe off any excess adhesive.

Dings and Dents: If your wallpaper has a paper back there is one way, if it has a fabric back we will have to use another method.

Paperback: Fill the dent with spackle slightly above the surface of the paper as it will shrink. Thats right, spackle the face of the paper. Avoid spreading it out any farther than necessary. Allow to dry and carefully sand flush using a sanding sponge. Seal the patched area with a little paste.

Now take a piece of the left over wallpaper and lay it over the area to be repaired until the pattern matches. Mark an area on the replacement piece of wallpaper,large enough to cover the patch appx 6" sq or so and cut it out. If the paper has a pattern use sizzors to cut around the edge of the pattern, an area large enough to cover the patch, nothing critical here,just follow the outline in a random fashion. You should be now be able to lay the repair piece over the patch and the pattern matches. No pattern of just background color? Good, that makes it easier, just cut out an area large enough to cover the patch.

Now take your repair piece over to the sink and soak it in warm water for 10-15 min. The backing will soften and you should be able to peel it right off. all you are left with is the face of the paper with the pattern on it. Take some of your thickened adhesive that you used for seams (see seam repair above), spread a thin film on the back of your repair piece and place it over the patch. smooth gently, clean off excess paste, roll lightly with a seam roller and your patch is complete. No one will ever see it.

Fabric Backed Paper: This method ( known as double cutting) can also be used on paper back if you wish. Same procedure as above for cutting your repair piece, match up the pattern and cut out an area larger than area that is to be repaired. This time we will leave it oversized, spread the back with your thickened paste, place over the area to be repaired aligning the pattern and allow it to sit for 10 min. or so. This gives it time to stick a little.
Use a straight edge razor blade or one of those handy zip knives and cut around the pattern over the repaired area or if no pattern just cut around the area to be repaired in a random fashion. Allow at least 1"-2" larger than the repair.
Remove your top piece, discard the excess and now on the wall you have a scored area around the repaired area on the wall, remove it and your patch should fit in place perfectly. apply a little more adhesive, smooth into place and wash it clean. Your done!