Sounds about right(
@Citrus). Staying positive is one of the more important ones, or at least avoiding getting frustrated.
If you feel you are at a standstill in your skills, try something new. It could be anything, weapons, gear, playstyle, practice differently.
I remember in the first month I was pretty amped up to get better and improve. That feeling has slowed down for me, which is probably why I am not thinking as critically or looking for ways to improve myself as I once did. Maybe taking a break from the game for a bit may help bring back some drive to get better. You may even be better when you came back.
Just keep on learning and applying the things you learn into your playstyle is a big one. If you aren't learning , others are. As time goes by, they chip away at increases in skill and you are left at the same place. The gap between skill is thus increased. People who are not seeing great improvement are probably learning the game at the same pace as the rest, resulting in the appearance of not much improvement. (Just a Theory) So learn, learn more and do it faster is all I can think of. Citrus already stated some key things to learn in the previous post. It is a conscious process, improvement does not just happen by playing all day. This goes for anything, if the technique is wrong or flawed, than you are only working on bad habits. FOCUS, but not too much focus that it engulfs your mind.