Read up and memorize. Stats, schedule, team history. And that entire roster better be burned into your brain, that's priority #1. After the basics are done, now you've got substitution patterns, strengths, weaknesses, etc. etc. As G.I. Joe used to tell us when we were young, knowing is half the battle.**
Pick a favorite player and study him. Besides giving you someone to cheer extra hard for, which is always enjoyable, it helps you sound more knowledgeable. Saying things like "We gotta get Omar Bravo some more touches here, let's go!" or "Watch out for Bunbury on this cross, this is his spot right here" makes you sound like you know what you're talking about, even if it's completely made up. Maybe Bravo is already dominating the ball, and doesn't need any more touches right now. Maybe it's not Bunbury's spot at all, but who knows? More likely than not, the person you're directing this bullshit to doesn't know for sure. You sounded cool though.
When in doubt, keep it simple. Along those same lines, at some point you're going to find yourself in some conversations with DIEHARD fans, and here's where you need to pump the brakes a little bit. You don't need to go blasting for the green with your 2nd shot on a par 5 from a bad lie (oh wait, that's the wrong sport. Still working on my soccer metaphors.) Let the real fan throw out all the opinions, and just nod and generally agree with everything he's saying. Don't go throwing out any crazy opinions that you might be asked to back up with facts. Also, when these real fans start making fun of the bandwagon fans (which they will, soccer fans are easily the most hipster-ish of all sports fans) you can chuckle along with them, but don't go overboard in your attempts to make fun of them; it will just result in more embarrassment if/when you are exposed as a poser. The guys sitting behind us at a recent game were mercilessly lighting up a few girls down the row from me, telling them things like "You know Sporting KC is the team in blue, right?" and "The reason they use their feet so much is because in soccer, you're not allowed to touch it with your hands." Rather than stick up for the girls, I nodded in agreement, and even threw out a couple of "Totally, bros. Totally." and some fist bumps. I was just glad they weren't making fun of me. (I'm not saying I'm proud of my behavior-but, you know....better them than me.)
Swag, swag, and more swag. How are people gonna know that you're a big fan if you're not sporting any of your new team's gear? By halftime of my first game in person, I was hustling to the concourse and shelling out a 20 scrill for some brand-new merch. Oh word, son? There was someone sitting in these seats in the first half who looked just like me? Couldn't have been me, I've had this shirt for months. Whoops, missed a tag there. Lemme pull that off real quick.
"I'm major league superstar Fred McGriff. Follow these simple steps, and you'll be a champion bandwagon jumper too."***************
**Speaking of G.I. Joe, I'd like to officially thank Bigsby for linking to one of these fake G.I. Joe public service announcements with the voices dubbed. I killed an entire lunch break watching every one I could find. For the record, this one is my favorite. The one you originally linked to took a close second. Thanks again, Bigs.
