you could always record a demo by typing "record whatever" in console without the quotations, and watch it later with "demoui" to see what you're doing wrong
just try to improve when you can and fix what you're doing wrong until there's a point where you can't find any flaws whatsoever
every time you die, don't just think, "oh i'm dead"
without first thinking, "why did i die? could i have prevented that??"
if you keep fixing things about your gameplay one step at a time, you'll eventually improve as long as you keep those things in mind for the future. i know a lot of bad tf2 players who have been playing for years, and they just don't care about if they die or lose and don't actively try to think about their actions because they just figure they're going to respawn or the map is going to eventually change. if you're playing mge/dm, just keep goals in mind rather than only playing purely to win at mge, work on aspects of your game, work on something and keep focused!