1) Recognize that every matchmaking game is NOT a pro game.
This may seem simple enough, but in my opinion it is the most harmful mindset to your average player. I can't count the number of times I've seen a carry get flamed for getting no farm in a safelane against a duo offlane, because the team ASSUMED that there would be an easy solo offlane because that's pretty much every pro game. Spectre-Crystal Maiden safelane does NOT beat Abbadon-Spirit breaker offlane. You can learn a lot from watching pros but you need to know how to apply what you learned correctly.
2) Keep an open mind
Pre-TI4 if you saw a razor getting refresher on your team would you flame him? Probably yes. Just because an item is unconventional doesn't mean it's not a good pickup. Ghost scepter, diffusal blade, and eul's are great examples of this. (Although pro scene publicity has gotten the word out that eul's can be great on every hero) So don't completely disregard picking up diffusal on anti-mage just because you don't get the mana burn, even though in 99% of games it's a bad pickup you are only putting yourself at a disadvantage by limiting your itemization.
3) Use your brain
I'm completely serious, no flame. If you have time to think about any action before you take it, you will naturally improve your game sense. For example if you are solo mid and about to jump the enemy mid player the first thing you should think about is: "What will he do in response to me jumping him?" Eventually this will become instinct, you will learn that you have to fake a spell or two before you jump a puck to bait out his phase shift. Keep pushing yourself further and further to try and read your opponents. "How will the enemy team respond?" "How valuable is the kill?" "could I be doing something more valuable for the team instead?" The ability to read your enemies will make you a very dangerous player and a GREAT leader, which will not only help you play better, but it will help your team play better as well.
Feel free to add to this list I would absolutely love to see what you guys have to offer as far as additional advice/criticism goes. Pls no flam tho ty <4
Source: https://www.reddit.com/r/DotA2/comments/2xvhew/how_to_improve_at_dota2/