Do you know how old the roof is? If not, assuming your jurisdiction requires permits for roofing work, you should be able to find the permits for the house and see when the last roofing permit was issued. Some areas let you browse all permits online (this is the case in my area), whereas others are more old-school and require you to physically go to City Hall (or similar) and view hard copies of the permits.

Asphalt shingle roofs generally last 20-30 years. If it's getting towards the upper end of that limit, you'll want to consider replacing it.

Try to keep trees trimmed back away from the roof if possible.