how can I improve as a tank is this game

Hi, I'm a plat tank for a while now because I don't play the game much(I'm the guy to reach plat in a game and just never play it again) but now I started to play the game again and started to take it a bit seriously and want to reach diamond and improve idk what to do like I know my characters I know what to play if something is bothering my team but instead of ranking up I just go down like I'm now gold 2 even and I don't remember the last time I was gold in this game it made me play support and I'm almost master from the placment matches alone even though I don't play support, I just want general tips if you can

summary if you don't care: I want to get better at tanking and taking space and what to do to reach Diamond and thanks in advance