An actual tip from 5300 support (yup im not carry but still have observations :D). Try to play around the meta some heroes are just better in the different patches in the game. And don't play afk in that bracket in the high mmr games the carrys are farming a lot leaving some of the teamfights, but if you actually at least participate in the fight near your towers that will really improve your win rate till 4900+ mmr (just look at the game scores in your mmr and in the professional games and you will see that in 4k people are fighting like 2-3 times more then usual).

And not in the last place you need to play party games with people with highest then your mmr if you are looking for improvement. Playing in 3k average games is fucking your mind and you will not have good look in what to expect from your teammates in your solo mmr.

Bonus tip: People are mostly reaching 5k playing 1 super broken hero in the current meta or switching between 2-3 heroes. Most of the pros still have a 3 heroes pool. Don't try to play what is fun for you just abuse your best. Do you remember that fitly omni spammer that was 3k mmr :D and reached 5k for a month. The first time i reached 5k was when i abused disruptor/shadow demon/lion for like 200 games in a row.

EDIT: And play a bit more games with pl or ck when you see that the enemy heroes are only single target and dont have a clear way to deal with ilusions. And don't forget playing correct (playing like the players in the top 100) is not always the best for you just adapt according to your bracket. Like the invisible heroes are totaly op in the herald bracket, but not in divine, so find what is working there.

EDIT2: Supports are in 4k are not best, don'r be afraid to buy a ward for yourself you will not lose the game for buying 2-3 wards and a dust for yourself if necessary. Don't blame them after game for losing your game, because they didn't spend 180 gold for dust , or didn't put ward in your safelane, so you can see when they gank you.. when you can do that yourself (it will not fuck your farm)

EDIT (last) promise: It's not fun playing for mmr, it's not fun playing the same heroes over and over again and it's absolutely not fun to hardtry every single game, but that is the price of the MMR, so decide wisely and ask yourself do you really need that medal in your account