Join a squad, as many said, stick with your squad, you'll learn from your squadmates how to fight. If you act alone you die too quickly and cannot learn anything at all. (and game is therefore not fun)
shooting skills are important, but the more important thing is teamwork, the former makes you a good fighter, the latter makes you a good warrior.
an example would be that if you suck at hitting your targets directly, you could pin them down by keep firing without much aiming. Then your teammates would have a easier time killing them.
A tip to stick with your squad is always wait for SL to spawn then spawn on him. Simple. I always do that.
a word of advice is that, for more advanced combat like smoke grenades/frag grenades, it is important to learn how to use them or else it'd be just harmful to your own team (like blinding your own team with smoke). Watch how your teammates do it would be definitely helpful.
"veteran" FHers like us have a library of tactics in our minds but those are really hard to tell in words. For example I could very often survive in a bad situation where all of my squadmates are dead, as there is a certain way to leave you undetected/unharmed, I tried to tell them to hide but they just don't listen/can't understand...
I always fnd MP easier than SP, lol.. simply because the bots can see you through solid textures...
and bots cannot be suppressed, and they have no fear of bullets. You cannot fool them as well (as they were too foolish already).
Oh btw, I always find surviving very important unless you have an army of backups/target is very valuable(tanks for instance). So you might see me sometimes doing suicidal landmine runs/the first guy to charge, but most of the time you see me just taking cover and firing from small observation holes. Glorious playstyles often leads to quick death.
Killing 10 enemies with your grenade would do like nothing if your enemy could recover before your team could take advantage of that. And why risk your life if you cannot help accomplishing any good goals?