This might be an unpopular view, but I think coming from the lower divisions the fastest way to improve is training your mechanical skills. Take a basic jump map like rj_rckteer, master it and try something harder. With soldier you are spoiled for game modes to train in, so play MGE, DM, BBall, Ultiduo and even aim maps like tr_walkway or the classic tr_rocketshooting2 until you are consistently hitting every shot. When you are playing these training modes constantly analyse your own play. Ask yourself what you could have done differently each life; did you just miss the shot or did you over-predict? Were you taking a fight from a bad position? Are you too predictable in your behaviour? You get the idea. Also find a way to play with players who are better than you on a regular basis, be it something like tf2pickup.net or find a nice group of mixers. Continue to apply the analytical mindset outside of training modes to team games, but don’t fall into the trap of blaming your team mates first before asking what you could have done differently, lest you become a toxic gamer :D

Roamer tip: watch flanks Pocket tip: guard your medic and do damage