Well, BF4 is both hard and not at the same time. Once you get the hang of it, it is fairly simple and somewhat easy BUT, before you get that. You're pretty much like a paper plane in a fire tornado hoping for the best.
Thing is, everything kills you, you just have to learn to not get killed. Just to practice, go in team death match with an assault rifle and get the Coyote Red dot sight, X2 magnifier, Muzzle brake to get less upward recoil and that angled grip to also help get less upward recoil so basically, now all you have to do is point and shoot. The x2 will help you if you have an ennemy at a bit of a longer range, also sometimes you get that glitch where the coyoto alone will end up with the x2 which is stupidly awesome.
Then, last but not least, circle around the map, especially the outer part of it. Try to stay away from the middle part where everyone is, try to stay in spots where snipers wont be able to see/shoot you. Make sure to always have some sort of cover around you ( Less exposed body) And to learn, medic is the best, you can heal yourself easily.
What this does is, almost everyone rush for the center of the map, while you circle around, so you end up flanking people most of the time and easily can pick them one after the other. Eventually, when you are good doing that, step it up, get the Scar-H with that exact setup. This gun has a small magazine but is very very accurate so if you switch it to single shot, you can do mid range very easily and dominate, use very little ammo and get a good Kill:death ratio, if you walk into a building or you think you're gonna get into a CQB situation, you switch back to auto. Worked very well for me. Then usually at that point you should be much better and know what you want and prefer.