Mw2 is my passion so if you have any questions about Mw2 iCan answer them for you. Here are my tips for Search and Destroy:
1) Always use a class that fits you. iUse to be guilty of not doing this, iUse to always use Marathon because iThought iMay have to escape pressure and it'll minimize my chances of dying. Then i started using bling and then use Lightweight, this class did not fit me. Because of this i now use the ACR w/ FMJ and Red Dot Sight. Stopping Power, Ninja, and a Semtex. Since i've been using this class i have averaged more kills per match.
2) Have versitile classes. If your on offensive you may have a different class then when you are on defense. iHave two different classes right now (#1) and one with Claymore instead of a Semtex. You can have different classes per map or for offense or defense if you choose.
3) Use previous round as a guide. If someone killed you at one spot before, more than likley they will show up there again, so either dnt go back to that spot or try and pick the person off and kill them before they kill you. Also if they were @ that spot in the first 3 rounds, chances are he will be watching that spot when the round changes so watch out if you are going to the same spot he went to.
4) Use Search and Destroy Perks! Dnt use Scrambler over Ninja or any silly things like that. For Search you wanna use Marathon, Sleight of Hand (if you think team will come in bunches), Bling, One Man Army, Stopping Power, Lightweight, (hardline IF you get streaks alot) (Danger Close IF you use grenade launchers) Commando, SitRep, Ninja, or Last Stand.
5) Mix it up. Try and get at least two starting points per map on search and destroy. For example is you are playing in Favela, try and have two rush spots for the start of the round. 2 for offense and 2 for defense. That way ppl wont kno where you will be the nxt round
Also another tip for S&D is that you need to get small killstreaks. If you are playing S&D usually you wont get many kills in a row. Now i use UAV, care package and a predator as my killstreaks. I recommend that you don't use a sentury unless you put in a place that w/o a doubt people will go pass. Wit a predator you can get a kill about 70% of the time, also people may come in bunches for multi-kills
*If you want anymore mode tips, post them in the forum*