Tip #1 - Contrary to popular belief, it's totally fine to talk to other girls you're with about anything at all. I love it when my girlfriend does this. It doesn't even have to be football related. As long as guys feel like you're enjoying your time there you're already winning.
Tip #2 - If the vast majority of people around you are standing for some reason, you should probably stand up too. Don't be the silent sitter. It's either going to happen because your team scored - yay. Or it might happen if your team is trying to stop the other team from scoring - in which case you just clap and woo to help generate energy.
Tip #3 - Absolute must is to thank whoever brought you to the game. Say you had a great time. Admit you don't understand all the rules, no one's gonna fault you for that. But, it's imperative for a host and/or male escort to know, er... think that you weren't just miserable the whole time.
That's all for this week. Plenty more tips to come, but I hope this helps at least one poor soul who is dying of boredom and borderline heat stroke this weekend. When you get a "thanks for coming to the game with me [pet name]" it'll be worth it because at that point you can do what all women do - leverage that into making your male do something he doesn't want to do.