I have clawed my way up from 48% WR to 59% and still improving (mostly solo). I only play above tier 7 and never anything below unless I'm grinding that line.
Winning is all about mindset. If you really want to win and play like so, it will reflect on your winrate. Also, playing high impact ships like USN Cruisers, BBs and DDs, Russian Radar boats and German Destroyers will also help.
Also, never giving up at any point of the game will matter. Some players give up the moment the enemy team has a 3-ship lead with 300+ more points, but skilled ones look at it as a fun challenge to do even better.
Some people say that playing for fun as an excuse to not improve, but I say to them: "Improving is fun because it wins you games, and winning games is the epitome of FUN."
In a sense, my winrate reflects on how much fun I'm having with the game.