When Bungie created Halo 3 they didn't have a good melee system in mind. So, as a result it can be rather confusing. It turns out that when jumping, you do 75% damage on the way up or down, but 150% at the peak of your jump. Here is a little known fact: you lunge when you melee. You can lunge about 1/2 the distance of a sword lunge, and you can use this knowledge to get the surprise on your opponent.
You can take constant headshots with a BR, so why do you always lose the fight? It's simple. Button-mashing. but before you attempt this, be sure you can consistently shoot somebody in the head.
Ever heard a beeping noise that grows constantly louder while in a warthog or other vehicle, then a few seconds later you inexplicably explode? That's a missile pod, with guided missiles following you. If you hear the beeping, get out. It doesn't matter where you are or what you are driving, but get out. The same thing goes for when you see a small red line on the side of your vehicle. Get out. Remember, one kill could change a game!
Going for an assassination with an active camo in lone wolves, only to be spotted? That happens because if the player you're stalking isn't a noob, he will be watching his radar for red spots. Even with active camo, they can see where you are on the radar. Instead of going for an assassination, just use your camo to surprise your opponent with a clip from a BR, before they can fight back, you have a kill.
playing grifball and you get smashed every time you spawn? Here's the trick to hammers, you swing your hammer before you would kill the person if you were both standing still. When is that? On your radar, there is the outer blue circle, and an inner light blue circle. the kill zone for your hammer is that smaller circle.
Tactics for grifball. At the beginning of a game, everybody spawns at the same time. Before you see the actual game, hold your trigger forward to walk forward and start closer to the ball. At the center of the arena, it doesn't matter how good you are with a hammer. It's all about positioning. Run around to the side of the enemy to get a surprise attack and kill them. Also, never, EVER, use your hammer to try to kill the guy with the ball. They can survive and be launched toward your goal. If you have the ball, it is possible, with good timing, to kill one person from the other team. You press "B" and punch them. If facing two or more, you'll be killed easily. Wait for back up to help you and don't be afraid to retreat.
Having trouble with the campaign on legendary? Just get 4 friends, preferably not noobs, and have one person stay back to spawn others at all times.
The meta-game achievements eluding you? You need 15,000 points in campaign to get them. Gotten it with friends? well that sucks because you have to do it by yourself. I recommend it on normal, so you do not constantly restart, with a few skulls on.
Always lose a sword fight? Can opponents hit faster than you? thats because they don't lunge and instead use "B" to melee twice as fast. Advanced players can easily recognize the appropriate times to use "RT" and "B"
Thank you for reading.