Halo: Combat Evolved/Blood Gulch

Blood Gulch Basics
Blood Gulch is the standard multiplayer map. It contains every weapon and every vehicle in the game. Two teleporters are placed in the center of the map on different sides. A sniper can be located on the left side of the map (looking towards Red Base). A flamethrower can be found in a cave area off to the right (by facing Red Base). Shotguns can be found in both bases.

Blood Gulch is best played as a 16-player Capture the Flag game. It also makes for some good Slayer competition. Blood Gulch is also arguably the best map in multiplayer Halo as it can be played on any game mode with any game settings.

Capture The Flag, Iron CTF, CTF Pro
For best results on playing Capture the Flag. From the start, send some guys to the middle of the stage, in between both teleporters with a Scorpian. Then send one guy to take Sniper Rock and another to get the Flamethrower. From there, send your best players forward to try and capture the Enemy flag. The Sniper should provide excellent cover and can spot enemy forces with ease. The Flamethrower guy should just hold his position while killing anyone that comes for it. Your flamethrower user should be the worst player on the team. If any enemies come through the teleporter you can easily use the Scorpian to blow them up. If you can afford it, have one guy defend your base, just in case anyone gets passed your Sniper/Flamethrower and Scorpian. Just keep up this strategy and hopefully you can win. Be careful of Warthogs, however, as your Scorpian and Sniper will be too slow to get it, which is why I said keep one guy at your base.

Team Slayer
No real strategy for Slayer. Just send some guys to the center of the Map with some Warthogs or other vehicles while sending other people to get the Sniper and Flamethrower. Have your Shotgun user(s) stand at the back lines. Have your Sniper provide cover and have your Flamethrower defend his position. If you have any more troops, just use them as you will.

Slayer, Slayer Pro
Every man for himself. Nor real tactic except for get the Sniper and Shotgun and get any powerups you can. Get the Scorpian as quick as possible and bail as soon as it's about to be destroyed. Warthogs are utterly useless.