Hi,
i really need to get better at halo 3. can u give me all the multyplayer tips you know.
Getting better takes a lot of patience, especially if you're completely new to Halo. The best advice I can give is not to worry so much about killing, but preventing yourself from dying. Whether it's Team Slayer or Team Doubles, 1 kill and 0 deaths is better than 10 kills and 15 deaths.
In terms of tips, depending on the map and the weapons you've got, it's impossible to say there's "one tip to rule them all" in any given situation. However, going back to the basics -- Don't rush in, and if you do make sure you take at least one of the opposing team out. Always hold back for a decent weapon -- Don't respawn and immediately rush towards where the enemy are with just the AR, at the very least have some stickies. Plan how you play -- Move around the edges of the map to cut down the number of places the enemy can attack you from. Battle Rifle's are hands down the way to go, if you're not confident with them -- Play nothing but Social until you're felling enemies with at least 6 shots. If facing somebody with a Battle Rifle, strafe.
Learn to do these naturally and you'll find yourself improving in no time. There is also lots of information on Battle Rifle proficiency and Strafing on the net if you're in need of a little extra help.