@jfkand @REI-LizH are right with their suggestions. One of the best techniques I have used is to go to your local shop and buy a trail map and describe your skill level and desired ride time/distance to an employee and have them highlight a few good routes for you. People are usually willing to share at least some well known trails and you get a map to remember your adventure and plan the next.
Sometimes you can look up trailguide books or find them at used stores. They might be a little out of date but can often get you in the right direction. Don't forget to check your local library first!