Two styles, rushing or hanging back, I prefer rushing tbh, learn the enemy run spots, get there quick and take out 2-3 players, the rest is easy work for your team or you'll get access to the rest of the team that have gone the other way and take them out from behind.
Some maps pay to hang back and take out those rushing but mainly the hit hard, fast approach works for me.
Claymores are great for cheeky kills and stay after death so a nice touch from the afterlife if you place them well.
Ninja pro a must due to heartbeat sensing campers but use the fast perks to get you behind the enemy and take them out as they will be focused from the direction they think you're coming from :)
also to add on to the rushing tips don't take short cuts try to take the longer routes cos you normally will get to see a range of people and also once you take out the rushers you'll be left with the campers so just flank em and easy kills for you :)
o.k., my usual class is ump45 silenced w/red dot, g18 silenced w/holographic, claymores, bling, cold blooded, and ninja. i usually rush unpopulated areas that look over the bomb plant areas which makes for good k/d ratio in the game which makes for lots of points.
Don't have any tips. 15-3 on Afghan is probably my best, but I hardly play S&D.
In COd4 I had developed strategies, but the ability to adapt is the main thing people need to learn. If you die going one way, try something else next time. Enemies will likely go the same way expecting the same kill, so surprise them. There may be certain paths to go on certain maps to increase chances of an easy kill. In COD4's "Vacant" for example, I always ran from the attacking side to the window on the left, then tossed a frag down the hall. If timed properly, someone running from the defending side would pop out the door and usually blow up.
You basically need ATLEAST 2 classes specifically for Search and Destroy.
The first should be silenced weapons + Ninja, the second should be the same (or similar) but with Cold Blooded as well as Ninja. This is so that if they call in a UAV at the start of a round you can quickly change.
Normally I use Marathon + Lightweight, not too many people use this in S&D for some reason so you should be able to get into position for either camping or rushing.
For equipment I would go for Claymores but frags or semtex do work as well.
Offense can be hard, normally I rush to about half way and take it easy, listen out for footsteps etc and only plant when its safe (or camp/defend when it is planted).
Defense is a lot easier than offense, usually you are closer to the bomb sites!
The key to Defense is knowing the map well, knowing where the enemy will typically go and then having half a dozen spots to camp. Yes... camp!
S&D can really be a game of patience, sometimes just lying prone and being very still will get you kills as people will often just run past and not notice.
Killstreak setup should be UAV, Care Package/Counter UAV & Predator Missle.