Curled shingles can be repaired by simply heating the shingle using a hair dryer and then, using roofing adhesive, flatten the shingle back down once it is warm and glue it into place. Place a heavy object such as a brick on the shingle for at least an hour to allow the adhesive to completely dry. Follow the manufacturers drying times and be sure to take temperature into consideration.
Rotten shingles or shingles that seem to just fall out of the roof can be easily replaced with another shingle. Several in a row can indicate a problem with the roof boards and should be carefully examined for water damage or rot. Always buy an extra bundle of shingles and keep on hand for these types of repairs.