Shingle roofs are not maintenance free. Ok for the most part they are there’s not much you can do for them except check for blown off shingle tabs or shingles, check pipes and penetrations for cracks and or holes. But more importantly if you have had work done by An A/C guy or had a new satellite dish installed you should probably get on the roof (if your able) and look at their work. Remember your A/C guy is not a roofer and they seldom call roofers to fix their work until they have a leak.
As you can see in this picture this A/C jack is not installed properly. What do you think happened here?
2. You should always have abandoned equipment taken off of the roof they are in many cases sources for leaks. In the case below this T.V. antenna is not used but it became a great roosting spot for pigeon’s and other birds. Their scratching around and poop has started to deteriorate the shingles around it. You can’t just replace those shingles a lot of times they are stuck together. So most of the shingles are in good shape and have lot’s of life left these do not.
3. Finally you should check for cracks in pipes and other penetrations at least once a year repair them as necessary to prevent leaks. Just put more mastic around the pipes and penetrations.