How can I improve my game from low-3k to 4k?

Hi everyone,

I have been stuck around 3 - 3.3k MMR for about a year now, which means that this is the skill bracket in which I operate. I think MMR is generally accurate, and as I have not moved significantly in over a year, I accept that this is my current skill level.

My question is - how do I improve? I watch my replays when I can, try to stay friendly in chat, stack and pull as support, watch pro games fairly frequently, got my last hitting/denying game locked down, and can play nearly every hero to some extent.

What aspects of my game should I focus on to improve? Like everyone, I want to play against the best opposition available to me.

Thanks in advance.