Brute Force

If you don't have anyone you can play with and you are forced to do this yourself, you can have a relatively easier time (and save ammo) by simply using Hawk (the Assassin) to kill one or two enemies while cloaked, then retreating to regenerate energy, then doing this over and over until you need the really heavy firepower of your AI buddies.

Have you wondered how to get squads for squad death match? Well what you have to do is get all the members of the squad. Like for the platoon you have to get Guther Ghent, Ty McTavish, Confed marine, and militia.

Unlock Confed Marine - Find the DNA sequence in Mission 1 or Mission 6
Unlock Feral Colonist - Find the DNA sequence in Mission 2
Unlock Feral Outcast - Find the DNA sequence in Mission 3
Unlock Seer Follower - Find the DNA sequence in Mission 4
Unlock Militia - Find the DNA sequence in Mission 5 or Mission 11
Unlock Outcast Shaman - Find the DNA sequence in Mission 7
Unlock Seer Priest - Find the DNA sequence in Mission 8
Unlock Feral Shaman - Find the DNA sequence in Mission 9
Unlock Gunthar Ghent - Find the DNA sequence in Mission 10
Unlock Shadoon - Find the DNA sequence in Mission 12
Unlock Fire Hound - Find the DNA sequence in Mission 13
Unlock McTavish - Find the DNA sequence in Mission 14
Unlock Shrike Soldier - Find the DNA sequence in Mission 15
Unlock Shrike Heavy - Find the DNA sequence in Mission 16
Unlock Shrike Hound - Find the DNA sequence in Mission 17
Unlock Hunter Lord - Find the DNA sequence in Mission 18

To unlock characters for Multiplayer, collect DNA containers stashed throughout the levels.