I go every single chance I get, watching it online will never come close to the live experience. A few pieces of advice I'd pass along:
1. ALWAYS buy a pit pass! No excuses! This applies to ALL motorsports, do it when you go to flat track events, drag races, motocross, stock car racing and anything else. The pit is your portal into racing culture. The smell, the noise, the teamwork and skill on display at every tent, and your only chance to really understand just how down to earth most racers are. These people aren't movie stars, they're giddy motorheads just like you and I, they just have bigger balls.
2. Bring ear plugs. Leave them out at first so you can understand why you might need them at some point. If you don't end up using them somebody you dragged to the race with you will be happy they're available.
3. Move around. Don't watch the entire event from one vantage point. Look at where other people have situated themselves around the track, there is a reason people are standing there, every corner provides a different experience, get up and experience them all, pick a favorite spot and watch the main event from it. Again, this applies to ALL types of racing.
4. Crashes, cleanup, and track prep are your opportunities to explore the pit. Watch for gasoline and fluid spills after a rider goes down, these take a while to clean up and you will have more fun exploring than sitting on the bench and staring.