A 'little bit' of advice
Attachments
My favourtie attachment is the dual mags it gives you double ammo so you can spray a bit more and every other reload is fast which is really usefull especially if your mag runs out when fighting with someone
Guns
like i said before my advice is just try what suits your playing style, also the map if its very open you not gunna want to use smg's and shotguns that much.
Perks
I always use flak jacket, sleight of hand, ninja
but if you dont use a headset i would recommend using tac mask instead of ninja and you dont really need hacker if you use flak jacket because you wont die from them that often so dont really need to see them
Killstreaks
Pick killstreaks that you think you will be able to get easily e.g if you die all the time and come out of games with a negative ratio a lot you dont wana use dogs but if you play and get a really high kd your gunna want to use dogs lol.
Also think about how you can use the killstreaks tactically call in a chopper when you have are defending something, e.g a planted bomb on demolition also for nuketown a napalm strike is really helpful as if put straight across the middle of the map on demolition it can cut of the other team from getting to the bomb for a couple of seconds which is extremely helpful, spy plane is really good because it helps all of your team and is helpful in all game modes
Equipment
claymores a prob the best choice
lethal
go with grenade or semtex tomohawk is fun but cant clear rooms
Non lethal
stun is faster than flash so i use that, nova gass is ok aswell because like the nova gas it denies the other team from getting to a point in the map, apart from that the rest arent very good, willy petes are allright for some things i suppose
As for tactics:
watch some youtube vids of some rushing tactics if you want but usually you get better at Cod by practice and experience but youtube vids help a bit and give you some good routes and spots.
oh yeah play it slow and tactical, think about what your gunna do and aim at the enemy dont just see him pop up and spray as much as possible take your time and it will pay off, try burst firing because there is a lot of recoil in that game,
and the most important tactic, dont get angry or you will just play worse as you wont think about what your doing properly if you get to the point when you start punching walls and trying to stick a controller up your butt you might wana turn of the xbox and go outside
and most of all have fun
cant think of anything else but if i do ill let you know :p