Step 1: Good Classes
Launchers are almost necessary because air support can be devastating
Flak Jacket is good because of grenade bombardment on objectives.
Hardened is also good because of head glitching and cover everywhere.
Marathon is good because it will allow you to run farther, to get to objectives faster.
Concussions are good for stunning enemys.
Claymores are easy to put at a doorway or ladder. They'll never see it coming.
Frag Grenades are effective because of buildings to throw over.
Step 2: Dem. and Search Tips and Bomb Sites
Demolition is a fast paced game mod. The bomb is around C3 and C4 on the mini map. It is a good idea to use tac inserts or marathon to get around the map quickly to plant or defuse a bomb.
Search and Destroy is a harder game mode. Your opening route can be deadly or stupid. You should, if on offense. Run right into the room where you can see the alley and the main house at C2. You should also be running down the alley through D2, into the building around the corner, throwing a stun, and getting into the building at C1. At B2, in the building there can be many campers defend both bomb sites. You should use a silencer on your gun no matter what.
Step 3: Domination