Recruit all 12 squad members to maximize your chances in the final mission. Each has a unique loyalty mission that unlocks their full potential.
Use cover effectively and pause to command your squad. Biotics can lift and throw enemies, tech powers disable shields, and weapons deal direct damage.
Your choices throughout the game determine who survives the final mission. Upgrade the Normandy, complete all loyalty missions, and assign the right specialists.
Soldier is the safest first run: Adrenaline Rush slows time and turns every fight into a shooting gallery. Infiltrator trades crowd control for the Widow sniper rifle and Tactical Cloak, which trivializes the Collector ship's Scion rooms. Vanguard is the hardest on Insanity, because Charge puts you behind enemy lines with no cover to duck into.
Do Zaeed's The Price of Revenge early - his fire grenade is the best area denial in the game. Mordin's loyalty mission unlocks Incinerate upgrades; run it before Horizon so you have them for the Collector swarm. Tali's trial comes after Haestrom, and Legion's loyalty mission needs the Reaper IFF, so it lands late - keep a save slot before that mission.
Assign Garrus or Miranda to the fire team, Tali or Legion to the vents, and Samara or Jack to the biotic bubble. Send Mordin or Thane back as the escort. Anyone not loyal dies during the hold-the-line phase, so take two squadmates with you and leave the rest to hold the door.
Upgrade the Normandy's armor, shields, and cannon before launching - each missing upgrade kills a squadmate on the approach.
Scan planets for element zero and iridium; the M-920 Cain is a one-shot heavy weapon that ends the Praetorian fight. Buy the Microfield Generator early - shield regeneration between fights saves more medigel than any weapon upgrade. A respec at level twenty costs almost nothing, so changing builds late is cheap.