How to improve my chess playing???

Ok, so I know that there are plenty of forum posts about this, and I know that there are many books on the subject. However, I seem to have a specific problem that cannot really be answered with "insert chess book here."
I will divulge:
I know that in the opening you develop all your pieces and take control of the center.

I know that the midgame is 90% tactics and using tactics to make my pieces superior and cramp in my opponent. I also know that one must make a plan in the midgame and try to determine what the other person's plan is so that they can stop it.
I know that in the endgame you have to make sure you are leading by pawns and (even better though it rarely happens) have a powerful piece advantage. I also know that you have to get the pawn to the other side to get another powerful piece.

My problem isn't "theory" or "tactics." My problem is "missing" things. I will sometimes stare at the chess board for a good minute before making a move, only to not realize a simple fork that my opponent immediately plays, or I will sometimes forget whole pieces that are under attack. I have done so much studying, but I just can't seem to "see" what my opponent is doing sometimes. I will often notice when it's too late to do anything about it. I do think ahead and I do analyze the board when I play, but I just seem to "miss" obvious things. 

What can I do to remedy my problem? I've tried chess puzzles but I still miss such obvious positions and superior moves sometimes. I know that everyone blunders, but I think my blundering is just insanely stupid sometimes. It surprises me since I've been playing chess since I was 6 years old and I have been studying the game for years now (books, classes, chess programs (including chessmaster), puzzles, openings, famous games, etc.). So what can I do?

Devise, for yourself, a list of questions to ask yourself or steps to take before you make moves; and ask yourselves those questions and/or take those steps each and every time before you make your move; even if the move seems obvious.

Here is a link to a blog post I made on this very thing:

https://blog.chess.com/blog/CaptainPike/before-you-move

Here it is, copied and pasted:

Wow, what a perfect reply. Never saw such helpfull post. Some title players need to take lessons from you how to help others. Well done. If only i had such guide years ago.

To @jpaluska, how much games have you played exacly over the internet and OTB... i don't see much on your 6y old account. Maybe you study too much without  playing or you are inconsistent in both and get to forget what you had learned and you make same mistakes over and over again...

Beginner players playing slow time control often get to get inpatience, so much rules they want to follow but after first dozens of moves they rush and make moves quickly.. they are easy to be provoked and they blunder horrible. Are you spending all of your time, or games are over with half of your time left om big slow time controls. 

You haven't solve tactic problems in that 6 years ~ only 26 and your rating is 800. Work on that. I think 800 tactic problems are exacly random messy position with heavy threats and free pieces to grab, exacly what you need to practice.

At beginning bullet/blitz chess helped me to quickly evaluate position and see all threats, hanging pieces etc. My board vision improved huge. So much random positions i saw, so much i learned like don't move until you check if that square is safe and so on and on. But you have been playing for 10-15 years, you already have to know that..

The basic skill you're talking about (OP) is of falsification. You'll usually choose a candidate move based on tactics and strategy... it becomes a candidate for its good points.

Then, you have to find all its bad points. This is very hard because it means finding the annoying replies our opponent can play which we don't want to do... we just found reasons why our move is good, we don't want to make it look bad.

But this is what experienced players do, so much so that it's an unconscious habit for them. The basic check is for all forcing moves. Find all the checks, captures, and immediate threats the opponent can play in response to your move. Particularly important are undefended pieces and a king that can be checked.

You play bullet, blitz and 10/10 with the computer.  You dont play any longer games at all that I can see, and dont play any longer games against humans.  Do you really give two bleeps about who beats who in your 23rd match against the same computer?  Just as importantly, do you imagine that your improving your chess by playing bullet??  You dont have time for a proper thought process in bullet, and probably not in blitz either, not at your strength, and you'll barely have time for a proper thought process at 10/10, and not even on all the moves.  So your practicing shortened thought processes when you have never learned to do the full deal.  Is it any wonder your not improving?

You need to play longer time control matches against opponents where your going to care if you win or lose, and you need to use your extra time.  Chess.com might call 10/10 standard, but you really want to be playing with at least 30 minutes in your live games and preferably 45+.  Correspondence style play would be great too, and is the way to go if you cant do over an hour in one sitting.  Post the games that you lose that you play at those time controls for us to help you with, and you'll learn something almost every time.  

I agree with what CaptainPike wrote, but you cant learn to do that process playing super-short time controls.

Study/Practice/Repeat    A key is to find the proper balance ( for you ) between study and practice/play . I studied more than I played for many years in the beginning but some players progress faster doing the opposite .  When you practice you should play stronger players as often as possible because you can learn from them even though your ego will take a beating . You wont learn much from beating up on weaker players . 

Gee, thanks everyone! I appreciate the help! Especially @CaptainPike for the detailed response. You guys really helped me out.

Oh my! What a helpful discussion! Thanks everyone for posting such valuable stuff. Special thanks to CaptainPike for the million dollar post. I will be grateful ever for this material.

I'll say what CaptianPike wrote may seem daunting at first but many players do a similar version of that thought process automatically (and more quickly) as they gain experience and increase their pattern memory. Yes you will miss things still from time to time, but over all you will be able to run through that thought process with little effort and time to find good moves after you gain experience. I'd recommend playing online chess to do it starting out, then move to faster Live chess controls. If you miss obvious things like forking possibilities it means you should increase your pattern recognition a lot, so set the tactic trainer here to unrated, lower the rating parameter to under 1,000, and solve those puzzles over and over again until the answers are almost instantly seen by you. It could take you hundreds of tries and that's fine. Just keep working on it while you play games using CaptainPikes thought process outline or similar.

another brilliant suggestion! thanks a lot Candidate35.