Always shoot hinges or locks instead of blowing them because it is quieter. Always crouch behind objects and make sure that your squad is with you shooting or you will easily die. Shoot through car windows, as they are a useful shield.
Unlockables
You can purchase these at the Special Features section.
ART Part I: Purchase for 10 Intel Points
ART Part II: Purchase for 10 Intel Points
ART Part III: Purchase for 10 Intel Points
ART Part IV: Purchase for 10 Intel Points
Increased Force: Purchase for 650 Intel Points
Invisibility: Purchase for 900 Intel Points
Once Shot Kill: Purchase for 600 Intel Points
Unlimited Ammo: Purchase for 550 Intel Points
Unlimited Items: Purchase for 550 Intel Points
Xbox Live bonuses
Achieve one of the following goals on Xbox Live to unlock the corresponding medal:
Biohazard: Retrieve the canister 100 times
Communications Specialist: 250 Total Conquest captures
Interceptor: Get 100 flag carrier kills
Mercenary: Get 100 kills
Perfect Attendance: Play seven consecutive days
Purple Heart: Get killed 100 times
Sapper: Plant 500 explosives (no kills required)
Veteran: Visit all modes on all levels for each mode (Total Conquest, Team Sharpshooter, Team Survival, and Retrieval)