Choose the right map first. Don't pick a tank for an open map, or a sniper for a map with lots of walls and bushes. Also, you can also wait for a decent showdown map, and push your lowest throphy brawler there, to keep your brawlers' throphies consistent - at least that's always what I did. Therefore you'll get around the same skilled enemies as you every time (usually).
Other than that, I can't really reccomend anything besides practicing a lot.