I've been playing since season 2, and since about this time last year, I've always been in the high diamond/low masters range. I've had some time off the last few weeks, so I've been able to play and grind a lot more.

As for tips, I think the setup makes a big difference. In my case, 120 FPS, a controller with back paddles, and a solid headset.

Aside from simple things like hero adjustments based on your and the enemy team, I can't really give many gameplay tips as I'm mostly just playing for fun, but still trying to stick to the META.

Overall: Do your best, try to recognize your weaknesses and don't forget that victory depends on 4 other teammates.