What to study?

I've known how to play chess for a very long time and used to be pretty good. After returning after a 15 yr break...I suck thanks to all the advances in chess instruction and youtube.

I would like to know where I should start studying to get better. My weakest point is my middle game and I frequently hang my queen when I get laser focused on something else. The obvious answer, I would think, would be openings. However, at my level, no one is playing tricky openings. It's all d4 or e4 basics. I feel like I develop pretty well and then lose it all in the middle game. Puzzles? All the puzzles I've been playing seem to be finishing moves. Is there a middle game tutorial?

All you're playing is speed chess, so you're not giving yourself time to think. 

Work on the basics:

General Ideas.

1. Stop playing blitz, and bullet.  Play longer time controls of at least G45, or longer.  
2. Follow Opening Principles:

• Control the center.
• Develop minor pieces toward the center.
• Castle.
• Connect your rooks.

1. Study tactics...tactics...tactics.  One of my favorite quotes is this: "Until you reach Master, your first name is tactics, your middle name is tactics, and your last name is tactics”.
2. Double Check your moves.  Before making a move, ask yourself: "Are my pieces safe?"
3. After your opponent moves, ask yourself: "What is my opponent trying to do?"
4. Analyze your games WITHOUT a chess engine, then have someone stronger go over the games, or post them online for review.
5. DO NOT memorize openings. Learn and understand the pawn structure, and piece placement for the opening you wish to learn.
6. Learn Basics Mates:

• K vs. KQ
• K vs. KR
• K vs. KRR

1. Learn Basic King and Pawn endings.

• KP vs. K
• Opposition

1. Have Fun!

Opening Principles:

1. Control the center squares – d4-e4-d5-e5
2. Develop your minor pieces toward the center – piece activity is the key
3. Castle
4. Connect your rooks

Tactics...tactics...tactics...

The objective of development is about improving the value of your pieces by increasing the importance of their roles. Well-developed pieces have more fire-power than undeveloped pieces and they do more in helping you gain control.

Now we will look at 5 practical things you can do to help you achieve your development objective.

They are:

1. Give priority to your least active pieces.

• Which piece needs to be developed (which piece is the least active)
• Where should it go (where can its role be maximized)

2. Exchange your least active pieces for your opponent’s active pieces.
3. Restrict the development of your opponent’s pieces.
4. Neutralize your opponent’s best piece.
5. Secure strong squares for your pieces.

Don’t help your opponent develop.

There are 2 common mistakes whereby you will simply be helping your opponent to develop:

1. Making a weak threat that can easily be blocked
2. Making an exchange that helps your opponent to develop a piece

Pre Move Checklist:

1. Make sure all your pieces are safe.
2. Look for forcing moves: Checks, captures, threats. You want to look at ALL forcing moves (even the bad ones) as this will force you look at, and see the entire board.
3. If there are no forcing moves, you then want to remove any of your opponent’s pieces from your side of the board.
4. If your opponent doesn’t have any of his pieces on your side of the board, then you want to improve the position of your least active piece.
5. After each move by your opponent, ask yourself: "What is my opponent trying to do?"

Thanks, I was not expecting tactics as I had in my mind that it is an advanced study. I really feel like that is where I need to start. Also didn't expect "don't memorize openings". Is that different than memorizing "lines" of openings?

You are right I need to slow down and recheck moves prior to moving them. 

Thank you, lots of good info I hadn't picked up before.

#1
"I frequently hang my queen when I get laser focused on something else. "

Always check your intended move is no blunder before you play it.