I suck at MW3 Multiplayer, Any tips?

Play more campaign to get the feeling of the game.

Get used to the maps more.(Know your way threw the maps)
At level 14, the guns might not be that great! So keep playing to be a higher level, so you can get better guns.
Perks- Try to make use perks essential to your game plan!

Camping could be a possible way (I dont suggest camping, because you have a bad perspective of where players are. And, at a low level, its good to explore places to help you kill)

That is pretty much it for tips at this stage. It all depends on what guns you use in the beginning everybody doesnt do good but keep playing. i sucked but now my kills are always between 20-45 and i die less then 10 times a match

Build A Hunting Field

When I arrive at my hunting grounds I make a prayer to the woods or the spirit of the wilderness asking permission and blessing to hunt on its grounds for a rabbit or two that I may have to feed myself and my family. I'll have a cup of coffee and contemplate which trails to explore then I proceed on my hunt.

My preferred hunting method is known by firearm using hunters as walking up rabbits. However it is slightly modified and this I admit this because after years of many rabbit hunts that came up empty handed, I have learned to tailor my walk up tactics.

Generally there's no secret formula other than to remember that when you are walking up rabbits with a slingshot you aren't trying to make the rabbits bolt from their hiding places because its less difficult to target the vitals a rabbit sitting still than it is to target their vitals with your slingshot while they're on the run. Patient and silent slow walks through a trail have often caused the rabbits to reveal themselves to me.