YEAH backatcha. I love soccer and MLS is particularly under-rated. That said, soccer is a tough sport to shoot. I assume you have a media pass/press pass for the game.
1. This will be a 10:30pm EST game. So at night, under the lights. You'll need fast glass with a high ISO to get decent results.
2. I have found that with soccer (unless you're going to ignore most of the game), 200mm zoom just isn't big enough, you really want something more like 300mm or 400mm. Otherwise you're doing to be doing a lot of cropping on photos. And with a fast 400mm, you'd better believe you'll want a monopod and a foldable stool.
3. How well do you know soccer? More specifically, how well do you know the two teams involved? The reason why I ask that is that each team has a number of players that you'll want to focus on. For instance, for New England Diego ***undez is their star player and they'll look to get the ball to him in attacking situations. For SJ, Steven Lenhart is not their best player but he is an attacking instigator (goes for a lot of high balls, 50-50 balls, does a lot of shoving off the ball, is involved in a lot of physical play and contact) so on corner kicks and balls in the box he's a good guy to focus on. Soccer itself is tough to shoot b/c it's a big field where the point of attack changes rapidly. Unlike football where there are a lot of static periods and the first 2 seconds of almost every play you know where to focus and have time to compose shots, not so with soccer.
4. Most of the time when I've shot a pro or college soccer game, I came out in back of goal to one side (so the net doesn't obscure the shot). It puts you close to the players. And corner kicks are somewhat as predictable as the snap/initial start of an NFL play (with usually the ball being crossed in from the corner flag in front of goal. You're going to be doing a LOT of anticipating. First time I shot a college soccer game, I hated the results. Oh, they were all in focus and crisp. But I got none of the athleticism or drama or fluidity of the play...they were all just pictures of guys in short pants caught in mid-action looking very awkward. So rather than look for a shot and then snap, you're going to want to anticipate and then shoot away. Get to the match earlier and shoot warmups (which are far more confined and static) and you'll see what I mean about awkward vs. athletic.
5. Okay, you're looking for specific shots to take:
--corner kick before the kick, look in the penalty area and you'll see guys manning up, lots of shirt tugging and grabbing, one-on-one duels without the ball, very confined in to space.
--during the corner kick or any cross (from the side into the front of goal) there will be players and a goalkeeper keeping for the ball, potential for very dramatic or athletic shots, also collisions and physical contact.
--free kicks near goal, the defending team will form a wall of players between the ball and goal. If you're able, shoot the facial expressions of the players in the wall and the kicker approaches the ball to take the free kick.
--the most athletic and extended times with the ball will be in midfield (so best changes to focus and compose play). Action in front of goal will be very quick. So if you want shots of someone running or cutting with the ball, you've got more opportunities in the middle of the field.
--there is almost always some drama and angst with players complaining/appealing to the referee so that's a good opportunity.
--if you're on the end line, the goal keeper is a natural area of focus. He's standing around for 95% of the match. The other 5% he's springing in to action, directing teammates, sprinting to balls, jumping in to the air, making stops, distributing the ball, taking restarts. In fact, take a few shots of the GK reacting to a ball with a deliberately show shutter speed (maybe 1/25th) so he becomes a colorful blur of motion.
--obviously if you can get a shot of a goal being scored, that's a winner (but that's tough to do at the moment b/c this usually happens very quickly and the ball is often played in to the penalty area, someone turns and shoots or makes a quick cut to receive the pass).
--symbolic pictures are also good. A shot of a ball in the net with the players a blur behind (or the goalkeeper laying in despair on the ground in the background). An empty stadium with cups and trash on the background. The supporters stands where a group of crazies will likely be standing and chanting and singing or waiving scarves during the match.
Best of luck, have fun, and bring back some winners to show us!