Asphalt shingles are one of the least expensive roofing materials on the market. While new materials help to make asphalt shingles more durable, they are not maintenance free. In order to get your roof to last as long as possible, you need to inspect your roof for signs of wear and make repairs as necessary.
Older shingles use tar paper impregnated with asphalt to create a water repellent barrier for your home. As the sun beats down on your roof, UV rays can leach the volatiles out of the tar, leaving them brittle and prone to cracking. If you have a roof that is fifteen or more years old, you should inspect your roof to see how brittle the shingles are. If the shingles refuse to bend, don't force them. The rigid condition of the shingles is a good indication that they are nearing the end of their service life. Replacement instead of repair should be the order of the day.
It is natural for shingles to start to curl over time. The problem with curling is that it may expose chinks in your roofing that water can leak through. You should be able to see curling simply by looking up at your roof from your yard. On a hot day, your shingles should be pliable enough that you can straighten them by hand and then stick the edges of the shingle that are prone to curling down to your roof with a dab of roofing cement. On a cold day, you will need to first warm your shingles with a blow torch so that you don't crack the shingles as you try to straighten them.
Large hailstones can puncture shingles. Stand in your yard and use binoculars to look for shingles that look bruised. On close inspection hail-damaged shingles should show a bulls-eye shaped cracking pattern. Once thus punctured, you have no choice but to replace the damaged shingles. Unless the hail damage is widespread, you should be able to extend the life of your roof by replacing only the damaged shingles.
High winds can tear shingles along seams or even rip them off of your house. If you have torn or missing shingles, replace them.
One of the benefits of installing an asphalt-shingle roof is that you do not have to have specialized training in order to make repairs. As long as you are comfortable walking on your roof, you should be able to repair curled shingles and replace damaged shingles on your own, but if you don't like heights or otherwise don't feel able to make your own repairs, you can hire a roofing professional like one from Sky City Roofing to make repairs for you.