Let me give you some advice for multiplayers.
BAL (assault rifle) best mid to long range gun
ASM1 (sub machine gun) best all around gun
or
HBRA3. (assault rifle) best all around AR.
Those are the only guns you want to use until/unless you get very very good.
Run 1 primary gun, 2 attachments, 5-6 perks and 1-2 scorestreaks.
Perk slot 1 - Low Profile and The movement speed one (optional)
Perk slot 2 - Cold Blooded and ... the other 'not appearing on radar stuff one'
Perk Slot 3 - Scavenger (optional until you get better and start running out of ammo) and Blast Suppressor.
Attachments, I suggest a sight and something to increase range/accuracy. either laser or foregrip.
ScoreStreaks, I'm fond of UAV with support, threat detection, and either extended time (HC) or scrambler (core), and then UAV with support and trap.
Anything that doesn't kill people as a scorestreak (except the sentry gun) can be set to 'support', which means your work towards them counts through your deaths, but it costs more to get.
Practice Boost-Dodging. either up, or to the side. Use it a lot when you run into an enemy. Boost dodge and fire at them the same time. Most people can't deal with that and lose that fight.
This post has been edited by Obdigore: 07 January 2015 - 02:45 AM