If they have the overhead cameras, definitely watch how the good players are playing to see how the feeds are behaving, how tight the tilt is, and what strategies they seem to be pursuing.
If they don't, volunteering to do some score-keeping is a good way to observe some play. And usually you get paid in tourney entries so it helps with the cost.
Plan to spend at least $150 if you realistically hope to qualify. And if there's a B Division, that's probably where you should set your sights for your first time.
Play your natural style. If you're doing poorly you might be tempted to try and copy other players' styles because they're doing better. But a tournament is no time to change up your game plan.
In most tougher tournaments, the games are set up to gimp the typical strategies, so be ready to look for the less obvious points. Again, observing other players is key.