Take the time to think about previous trips you have been on; be sure to make a note of all the positives and negatives. Deciding where to go is only the first of many steps in the planning process and 'managing your expectations' is possibly one of the better approaches.
Flexibility is key when it comes to travel, it's good to keep a contingency plan on hand for any issues that may arise due to things such as inclement weather.
If you only have a limited time to explore your destination, you may have to make sacrifices when it comes to ticking a few spots off of your list. If you are someone who would rather take your time to thoroughly experience your destination, be open to trying new things and/or stepping off the beaten path.