Remember, you asked for it!

I've been working on this, and it has helped me a lot. This basically becomes part of your PSR. It's basically a transition from thinking mode to performing mode.
You have to have some trigger to go into "shooter mode." Plan while up, I don't care how you do it, be it just looking at things, performing calculus with diamonds, thinking about a pink hippo... whatever. At some point you must make a conscious decision on what shot to perform. Figure percentages, do whatever you need to do. Make the best decision and convince yourself this is the best option. Sometimes it's hard and you have to practice a good BS meter on yourself.
Choose one option, preferable the best option.
Once you've reached the decision and not before, do whatever you need to do to get into shooter/performance mode. Now is the time for your trigger. You must go from an analyzing egghead into stone cold shooter mode. Bang the chalk on the table, snap your fingers, feel the wind on your face... whatever. I prefer breathing in fully to extend the diaphragm and then breathing out fully. It releases tension in your body/muscles/makes you steadier. Once I breath out, it's go time... into shooter mode. It's greatly simplifying things but think of it as a light switch in your head.
Now when in shooter mode you can't worry about things, it's all about performing the shot you chose to preform. Don't worry about the shooter's feelings, he's there to perform and shoot whatever you told "him." Be a robot that follows the instructions you just decided on. There is no room for doubt, do what you instructed the "shooter" to do.
Now if while in shooter mode your mind isn't clear, have a bad feeling, etc. get back up, go into egghead mode, re-evaluate the situation, make up your mind, be if for better or worse, throw some chalk on, do your "trigger" then shoot the shot in shooter mode. Basically you must be fully committed to shooter mode/execution phase. Feel the shot, feel the cloth, feel the air currents or whatever. You're wanting extended body awareness so you can perform the sweetest stroke ever. Feeling while in shooter mode is ok, but thinking and being scared of an outcome is not. It's like if you think "don't scratch" you are more likely to scratch. It can be tough but while in shooter mode shut your head and inner dialog up. At most you could be thinking "pure smooth stroke" but you even have to be careful you don't get carried away with this type of thing.
And stay down on the damn shot and watch what happens. You can learn a lot while watching the balls with a clear mind. It allows you to readily adapt to table conditions, ball cleanliness, whatever. If you don't observe you're shooting in the dark.
I imagine for some this seems overly simple, but it can be a real struggle that takes dedication to achieve. Think back to your last dumb mistake... likely your head wasn't quiet and in "shooter mode" when the mistake occurred. You were at best undecided or maybe even worried about an outcome. And remember, mistakes happen, you gotta let that stuff go. I mean try to quickly understand what happened but don't dwell on it or beat yourself up. That's just sharking yourself and this game is hard enough without mental attacks on yourself.
Another way to put it, you know in cartoons where the little angel and devil are on a guy's shoulder? Don't listen to either of them while in shooter mode. Let them fight it out while in the planning phase and don't believe any BS you hear that doesn't match reality. We're great at self sabotage and thinking while performing a shot is one great way to sabotage your game.
Good luck and remember to wash behind your ears.