* By no means am I an authority on how to shoot anything. These are just things I do to make my life easier.
Get there early:
You'll notice that I favor getting to the venue early. It just makes life so much easier. I like to arrive about 1 to 1 1/2 hours early if I can.
You will almost never need a lens wider than an 80-200 with baseball. I usually just take a 400 or 300 to take care of the infield and pitcher. This sort of depends on the stadium since some places have the photo pit 10 yards from the first baseline and others have it more like 20. That 10 yard gap makes a difference between which lens I'll take. The 80-200 is for shooting the dugout on my side in case anyone goes bonkers and decides to break a bat over the railing, or if a catcher slides in for a foul ball. I strongly suggest not taking a wide angle lens because it will only tempt you to run onto the field after the game for jube. Doing this will most likely lead to you having a colonoskopy performed on you by the other photographers at the game. More on this later.
Don't be afraid to use a 600 or 800 for baseball. Not all the action is limited to the infield and some of the better shots I've seen have been from the outfield as guys are jumping up against the wall to try to snag a homer. Once you get the hang of it, you will be pleasantly surprised. Photographer Brad Mangin has had some nice stuff of guys up against the outfield wall in Sports Illustrated. I'm not sure if he was shooting from the dugout though.
Tripods and remotes:
Logistically, baseball is the perfect sport for remotes. Like basketball, you know where the action is going to be most of the time -- either under the basket or on one of the four bases. It's not uncommon to see someone sitting in the dugout with four foot peddle remotes and a 400 in hand to "go fishing" with. The easiest way to do this is to just plop a tripod down (OUT OF EVERYONE'S WAY) and stick a 300 or 400 on it. Of course most people can't afford four or five 400mm's, so pick which base you really want to shoot if you are going to do it with an extra body. The easiest base to shoot is second. It's always good for double play photos of the short stop jumping up in the air to throw to first, while the baserunner is sliding beneath him. Home plate is good to for those collisions.
Both for you and your camera. I suggest the ones PhotoFax sells and they are the only one's I've seen. They are $65 but will save your lens from needing to be repaired. As for you, Mountain Hardware makes some great four season waterproof shells. They're not too expensive, but you can use it all year round. I have a non-insulated one that I paid $420 for, but it's meant for skiing or kayaking, both of which I partake.
My favorite spot:
I'm personally a big fan of the first base line. I can get the double play shot mentioned above easily and with the short stop throwing towards the camera. I can also get shots of the lead off runner at first diving back when the pitcher tries to pick him off. I'll usually shoot this really tight . . . Say from the first baseman's knee down. I also like it because I usually try to get the ump or ref in my photos to get their reaction, and when there is a collision at home the ump is normally on the third base line side of the plate to see if the runner is safe or not. So I'll have a cloud of dust, two players lying lifeless in the dirt with broken femurs and busted noses with an ump over them with his thumb over his shoulder. Well, at least I got that one time.
Another place I like is in the stands behind home, or in the outfield stands. With a 600 and teleconverter you can get some nice shots of the batter and interesting angles of the action. From behind home, you can use a shorter lens, but still get nice angles of the pitcher and of the action.
Make sure you are keeping track of the pitcher's performance. You don't want to get a phone call from your editor in the ninth inning asking if you have anything of the pitcher because he is pitching a perfect game, and not have anything of him. It's common practice for most folks to shoot each pitcher when he gets up just in case.