Small holes, tears. Lift shingle carefully and put a dab of asphalt roofing cement under the hole. Press shingle down into cement.
Badly torn shingles. Cut out the damaged tab. Cut new shingle to proper width and long enough to fit up under cut-off shingle several inches. Smear asphalt roofing cement on bottom of patch and set in place. You do not need to nail a patch unless it is two or three tabs long.
Curled shingles. Anchor tabs with asphalt roofing cement.
Mineral surface gone but felt intact. This is not serious but is unsightly. If mineral surface is gone only in small spots, collect minerals that have washed off into the gutter or scrape them off a scrap of shingle. Dab asphalt roof coating on the bare spot and scatter granules thickly in this. If a large part of the surface is gone, paint the entire roof with asphalt roofing paint which comes in various colors.