Relax, stay cool and don't get uptight. Enjoy the weather, the music and the people. If you don't like crowds, stay on the outskirts. The sound is usually pretty good even way at the opposite end of the big stages. Don't be afraid to go directly into the crowd.
Pacing is everything.
Take your time. If you see a small crowd looking at something, check it out. If you work in production, you will meet some of the artists. Those are very popular jobs and they go first. You need to be quick and flexible to get the best positions.