Here are a few things you should do every year to keep your roof in good shape:
1. Clean off debris, which holds water and causes deterioration. It collects behind all penetrations, like pipes, the chimney and skylights, as well as in valleys where roof sections meet at an angle.
2. Inspect the flashing to be sure it is solid and not deteriorating. Seal if need be, removing all old caulk and scrubbing the area clean.
3. Secure loose shingle tabs with a bit of roof cement. Replace damaged shingles.
4. Clean, inspect and secure the gutters. Replace if they are deteriorating and have holes in them.
5. Inspect and repair the mortar on the chimney.
6. Prune trees branches that touch or hang over the roof. This keeps them from rubbing on it, but also keeps squirrels and other climbing animals away from the house.
7. If you have any serious damage, hire a roofing contractor.
Source: Build Direct: