I get awful teammates occasionally but im so ownage it doesn't matter.
Honestly, the biggest thing that I did to jump mmr was to stop focusing on my teammates. Like I used to believe in my teammates and just go in assuming they could do something, but its honestly much smarter to just pick high impact heroes regardless of role. Here's my quick go-to list for winning ranked by farm priority.
1: ursa, slark, wraith king, lycan (if ur disgusting), void
2: invoker, ta, storm, tinker, bat
3: centaur, phoenix, timber, tide, nyx, potm, puck, dark seer, omniknight
4: sand king, earthshaker, tree, tusk, aa, visage
5: dazzle, rubick, rhasta, lina
Honestly I think offlaners and 4 position heroes have the biggest impact in ranked matchmaking, and that's just simply due to their nature. Sure you can win your lane mid and snowball, sure you can farm so hard that you bury the enemy team in gold, but there aren't many heroes that can do that regularly and dota at the end of the day is a 5v5 game. There will always be someone that picks a greedy safelane like AM, and mid has changed from a gank-oriented lane to a farming lane, so you can't afford to leave too much for ganks because it just makes you fall behind the enemy mid as you watch your team fall apart.
If you can play a really good offlane, you not only end up going even against their dual or trilane, but by playing these kind of heroes that can do alot of damage with just levels and an item or two you can really shift the game towards your team's favor while not playing a farm dependant hero.
4 position heroes like sand king or earthshaker also do really well because of their large aoe presence with no items, and their terrifying teamfight potential with one item.
Playing self-less support is fine if you want to be a good samaritan, but if you wanna win your best bet is to play a hero who can do enough for your team. Because really, most players in your mmr bracket are there because they belong there, and can last hit and execute simple things to the degree required by your skill level. If you really think you're better than people in your skill bracket, pick heroes that can actually do stuff and see for yourself whether you belong there or not.
I probably missed a hero or two, and obviously this list is just based off my own preferences and skills as a player, so feel free to sit down and compile your own list if you're serious about winning more or mmr climbing. But the fact remains that matchmaking isn't some big brother ordeal where they punish you for winstreaks, its simply what it is, matchmaking. If you're better then your pool, pick heroes that can show it and you'll see results. If you belong there, well guess what buddy you're gonna win some and lose some.
tl;dr: pick good heroes that dont have to rely on teammates if you think you're hot shit and see what you can do.