Only take bolt classes, or SMGs if they're plentiful (i.e. Lyes Krovy)... turn your resolution up as far as your computer can handle it without any lag, and look for little dots on the horizon to shoot at. Don't bolt immediately after you fire so you can see by how much you missed and adjust your lead. Once you got it down, you can bolt immediately after firing. And don't think bolts are the "worst weapon" or something. I take it probably 80-90% of the time by choice. It's deadly once you learn to aim. When you do pick up something else, SMG, semi-auto etc. learn to know its ideal range. Don't waste your time trying to fire an MP40 at a bolter 200 meters away. You're better off zig zagging from cover to cover and closing with him. Same with semi-autos (longer range than SMGs obviously, but not one shot one kill like bolts at pixel shooting range generally)
Oh and get in the capzones. Yes you have a rifle, but you can still one-shot a dude with a 71 mag PPSh if you're lucky (hip shooting just comes with practice). Don't sit back and take potshots. Especially if you're a newbie, you're just wasting ammo/time/your life cause you can't shoot for crap for at least a month (much longer for many). It's different for a dude who's been playing for 5 years and has pixel shooting down pat. (though everyone should always be advancing of course... unless you're defending, though personally I like to "defend" a lot of times by getting on the extreme flanks and shooting them from behind from behind a bush or something with a captured enemy weapon---so the sound doesn't give me away)
One piece of advice. If you come across another bolter within say 25 meters... don't try to stop and aim, hip shoot and charge him (I always attach bayo). I've killed so many dudes that tried to aim at me like that it's ridiculous. At that range ironsights are more of a hindrance than anything. If you stop it makes you a very easy target for hipshooting. Keep moving sideways or whatever, fire, then rush in and stab his *** if you missed. (make sure you're sprinting when you do, if you hit him without sprinting it usually won't kill him, you'll need 2 stabs).
Learn to throw nades. Nades are crucial. Learn to get them into windows, learn to airburst them (by cooking them) over trenches. Remember you can bounce them off walls (durh). Generally you always wanna cook your nade at least a second or two unless you're going for a really long toss, otherwise it gives whatever bad guys near it a second to prone dive behind a piece of furniture or something.
Oh and don't even think about taking sniper, squad leader, AT soldier, MGer, or tanker (if it's a map like Leningrad with one or two tanks... if it's arad obviously go for it if you want), or people will verbally rape you over chat and VOIP.
If you wanna practice those weapons, practice in SP, or, the better method, follow the sniper/whatever around and when he dies pick it up and try to do something with it. (not bolting immediately after firing with a scope is especially helpful as it's very easy to see where you bullet landed and how far off the mark you were so you can adjust for the next shot).
Unfortunately the bots travel in more or less straight lines or very predictable patterns so it's not very good sniper practice for newbies...
As for bolt shooting. I've found always shooting one pixel (in ironsights) below the target almost always gets the kill when the target is 150+ meters away. Of course it's different at dif ranges, but that's just a general rule of thumb, could be helpful
.
Also, don't use voice commands EVER if you're somewhere where the enemy doesn't know you're there. If you're in opposing trenches/buildings/whatevers and there's bullets flying everywhere and nades going off constantly that's different... but if you yell some retarded crap while you're creeping around you're just giving yourself (and nearby teammates) up basically.
Oh ya other thing, if you see a big pile of nice shiny weapons, sniper, MG, whatever and they're all in the same spot, DONT GO THERE. RESIST THE TEMPTATION. Should be obvious but it's hilarious how many times I see people on pub servers do this and get shot over and over by some dude with that spot ranged in perfectly.
Last little thing. Prone diving. Very useful. DH has mantling now, but prone diving is still faster. Just sprint, and hit the prone key at the exact moment you're about to run into the object. You'll land on top of it. Very useful (though considered an exploit a lot of times in clan matches, but in pub servers, who cares).
EDIT: Can't believe I forgot this. RO shooting 101, always always always try to shoot from a supported position if possible. Especially as a newbie you won't be able to get a good shot off while your gun is swaying. Even the PPSh with its insane recoil turns into a mini-MG when you're prone and have it on the crest of a hill or something. Turns into a death dealing machine even at range. Always keep an eye out for supported positions while you're running around.
I'd also recommend fiddling with the mouse sensitivity settings till you're happy with it. It makes a big difference. Personally I use 2.25.
Well that was long. Hope you get something out of it.
Oh and don't be a dumbass and block doors.