1. Not getting to the parks early enough. Go early in the day and beat the heat, the crowds and the lines.
3. Not doing some pre-planning and not having a map. Have some sort of a plan or you will be spending your time roving around aimlessly. Get a map and schedule for the day as soon as you get to a park. Then look at it to see what parades, shows, etc. you don't want to miss. Time can get away easily when you are having fun and before you know it you missed something you really wanted to see.
4. Not taking a midday break. Give the kids a chance for a nap or you will pay dearly later. Some time at your resort enjoying the pool will give everyone a chance to cool off and you will be ready to stay up for the fireworks later.