one thing i learned when climbing from 2.8 to 3.9 before dropping back down to 3.4 nowadays, is your role must be flexible, can't keep playing same role.
However, on the other hand, i noticed that if you too extreme in one role (in my case support) when you meet a team that is all the same role, you're pretty much fcked.
There were countless times when i reach the MMR ceiling only to meet a team of support players 5 supporters looking at our stats (last 20 matches) nobody could farm effectively, nobody could use tank effectively.
Then we all suffered from -25.

highlight point above, always get a TP, but know when to use it, do you need to go there immediately or can you walk out, it's like when you died and nobody is pushing your lanes, is it necessary to TP? maybe that TP out immediately after someone needs help and you can't TP over cause 70sec cd.
Dotabuff always give useful tips register yourself if you haven't already.

If you like variety and you suck at critical time during MMR ceiling, the only way is down, so better to concentrate on your good heroes and make sure you reach that ceiling. I've seen some really good players throw games because they got bored of using their good hero. They think that they already know it all, and chose to 'random'.
I'm not against variety, but not during MMR, spoils the game for others trying to climb expecting the full teamwork of all their teammates only to have someone on their team go random and then say, sorry guys i can't use this hero anybody wanna swap? or worse, just think they can and feed.