After you know a bit on the theorycraft, now you have to play some games. An important thing to understand is that one game consists of playing it till the end. You can't make a good start and then make some bad mistakes like losing all your heroes(non-NE,xD), then lose because of it and say: "Not fair, I played better." right?

Example1: Let's say you are playing versus ORC on Turtle Rock and you want to play the DH+BM+Tinker combo with a few archers in the start and then the favourite mass DoTT. You made a good start - good harras on the orc hero, you saved some archers if he had attacked you and all is fine. But then you make some mistake and he gets advantage and in a few minutes he is able to use this advantage and win the game.

Where is the mistake? How come you played better in the start and then lose the game? Pretty simple. As it seems in this situation your mid-game isn't as good as your early game.

What to do? Concentrate on your mistake.

How? You may want to write down your mistakes so you can view them later or just save the replay. When you start the game and you know that your mid-game is on lower level than your early game, keep concentrating on this issue. Change something, make some different move. Study what you made wrong, compared to other NE players in mid-game. Investigate your mistakes, and keep changing untill you fix it or change your style to something different that helps you.

Example1: when you hit Tier2 and you have to push him with Beast Master in his base, but during the attack you lose your hero or more units that's is not normal to lose - train the same situation a few times, if you keep making the same mistake, watch the replay again. Concentrating on a given mistake you make in your playstyle will help you improve overall. When you take a look in your Orc versus NE match-up and see that you are not good in it, try to fix the mistakes one by one. Don't try and to fix all of them at one time. Better fix one thing and learn to do it the best way possible, than doing more things on an average level. This was only an example and there are a lot more situations you will need to learn, but if you take it one by one you will be heading forward, not staying on the same level of MU for a longer period of time.