HoW Do I Improve My Mid Game Chess?

do puzzles

a lot

so you can recognize tactics

Most if not all my puzzles are back rank mate for no reason at all. And if it is not back rank mate, it's often positions I will not reach.

This mainly due to the fact that I always play Vienna gambit accepted when I am white and Pirc, Modern Defense or Indian Game as black. Those positions are all theory (except for Vienna) and no mistakes until my opponent does something new that I have never seen before and then I blunder everything for no reason

Read Pawn Power in Chess by Kmoch.

Dear Forgetful_Guy

I am a certified, full-time chess coach and International Master, so I have seen it and tried it all.
There are so many ways to get better and I know it can be overwhelming.
You can learn from free videos on youtube, there are books at your disposal that can all help, but they are not tailored to your needs.

One of the most important things you can do is to analyze your games! You must learn from your mistakes! That is a priority. You can't really move on to a new, different topic and learn new ideas if you still make the same mistakes over and over again!

This is where a chess coach comes into the picture. A good coach can show you how to study, what to study, gives you the material YOU need. Naturally, it takes time to use everything in practice, but if you are relentless and persistent you will succeed!
You should learn the main principles in every area of the game (opening, middlegame, endgame).  Don't focus on only one part! You should improve your tactical vision as well as it is part of all areas!  
This how I built my training program for my students. We discuss more than one topic during a lesson so it's always interesting and they can improve constantly. I give homework too and the right tools to make practicing enjoyable and effective!
Don't worry about your rating and the ups and downs! Just keep on playing and practicing!

I hope this helps.  I wish you good games and 100+ extra ratings