Having played video games for 35 years and been a counter-strike veteran for 15 of them, I have a good idea of how to aim, how to handle various weapons and how to get on top. So far in FC3 I've level 20's all my main guns except for the sniper rifles and secondary weapons which I mostly play with now. On full servers i've come top using pistols only, all the shotguns including 1887 and even as a sniper.
With so much negativity surrounding multiplayer, I thought I'd give some tips as when it works it's a good blast and everyone ought to experience the treat of kill streak after kill streak using their favorite weapon.
1. Get to know the maps. If one is not fully familiar then run around it a lot to get used to it. You don't stand a chance of camping out with a sniper or ambushing if you're not aware oh how an enemy will flank you.
2. Moving a lot at speed will keep you alive. You might get caught in fire but if you cant see who's firing then keep sprinting for cover.
3. when killed always try to stay for a revive. You'll get team support points if revived and upon which immediately hit your battle cry for more.
4. Always use battle cry. In addition to fortifying your team mates, you get team support points.
5. If nobody on your team is using scouts then do it yourself. So long as your team can see enemy locations for most of the game then you yourself will have a better chance of staying alive.
6. Always try to revive your team mates even if it means you'll probably get killed. By keeping them alive theres a good chance they will do likewise. This rakes up everyones team support points keeping you all in scouts, gas and barrages.
7. Best loadout for maximum kills on most maps:
Primary weapon - MP5 which is very familiar in all shooters and very decent in this one. Warrior mod, Hot rounds and extended magazine. Run constantly to get enemies close. Never aim or look at your recticle. Fire full auto on enemies when they are in the middle of your screen, while moving yourself.
Secondary weapon - Bow with fire arrows. They give you range when you spot an enemy too far to take out and act like a long distance molotov, often catching several opponents in the fire. Always aim at the floor or an object by them which you obviously won't miss.
Equipment - Light body armour and proximity mine. Each time you spawn make your priority setting down the mine in doorways or near fuel barrels, anywhere an opponent is likely to be running past. Nine times out of ten you'll kill at least one opponent which makes holding on for a revive rewarding as usually it's just a matter of time before someone gets nailed by it (mines are removed from the map when you respawn).
Skills - Snap Shooting as you use the MP5 in that mode, Speed Burst as you want to be too fast for someone to hit.
Battle Cry - Haste as you want your team mates to be able to keep up with you in order to revive you and stay alive themselves.
8. Shotgun - marvelous fun taking out a group of enemy one shot at a time. The trick is to move by strafing, having your crosshair at head height and waiting until it's on the head and blam! Likewise if you're stationary and see an enemy run past - line it up head height ahead of them and blast as soon as their head passes by your recticle. Full damage mods but the barrel is good to narrow down your cross hair size.
9. Assault rifles - brilliant using iron sights at range, stand still, aim at head and very short burst. move, then repeat. full damage mods as you should only burst fire unless close counters then shoot from the hip and pray.
10. Heavy machine guns - the only weapon i find that benefits from using a scope (apart from snipers of course). I find these more accurate using full damage mods and fired in very short bursts at any range crouched. Never use full auto as hopelessly inaccurate like that as they ought to be.
11. Sniper rifles - Still trying to master these myself. Can be quite inaccurate however if you've taken to using these then you probably know them better than I do (never was any good with them in CS!)
Hope this is of some help to those getting to grips with multiplayer. It often is frustrating with the bugs, issues and players owning the maps but when you get a good game it's a real good blast. The MP5 loadout will have you scoring well before long.
I just find it a shame when top ranked players persist with using that, the BZ or P416 as they are easy guns to use. Often those wanting to brag about their kill to death ratios merely have an agenda for owning n00bs as they put it and have hardly a revive to their credit. We all enjoy a mad map doing it of course but it shouldn't be game after game - I prefer to give others some sort of chance.
Thats part why I prefer to master the other weapons as above all, theres nothing like winning a map having greatly helped your team and used a much more difficult weapon. Your kill ratio may suck but you demonstrate better skill for it.
One other thing. Mercy at the end of a map shows your true character.
Edit - please feel free to add tips that work for yourselves as we all have different playstyles.
Knife btw springs to mind - if out of ammo or dont have time to chamber another round and an enemy is close then gun for him with the knife! The knife key ought to be the next easiset to hit after your shoot button.