wanted to post too, but alot has been said before.
1/ if u are a right hand shooter, always straighten your left arm. make it 180° and not 160° . no idea why, but it helps.
2/ use chalk after every shot. not only does it give me 3seconds to relax, but also makes sure ill almost never miscue. as im a fast player, i had the bad habit to forget about the chalk. i was SO concentrated on positional shots and potting i forgot to chalk
3/ play the table , not the man. (i had played a guy before i know is better then me, for some weird luck reason, i had to play him in EVERY qualifying round i had this year) last time i played him. i didnt even look at him. not seeing him or his freezin cold un-emotional face scared me. he's a A player, where as i am maybe a B, more a C player. i managed to get 3-7 in front. after that when i realised i COULD win, i screw up and lost all the remaining frames.
4/ dont use englisch, draw if u DONT need to. i had the habit to use draw on almost every shot. and just use the speed to compensate it.
5/ the perfect speed. not really sure about how to explain this... for myself it seems that at one certain speed, i rarely miss a shot. if i play slower or faster, i do miss more often. i call it my-own-perfect speed. even 5% faster will make me miss the shot more often. the speed has to do with: its slow enough for a ball to fall in a pocket, after it has hit the side of the pocket, but hard enough for a non perfect flat cloth having no influence on it. its not to fast for the ball to stay in the jaws, and not to hard so i miss hitting the cb exactly where i want. (control)
6/ walk to the ob i want to pot EVERY Time. and check it from another angle. it makes me walk 10miles more /day then normally, but it gives me time to put the chalk, and just adjust my plans while standing up.
7/ if my cue isnt gliding well cuz my hand is 5% more sweaty then normal, if ANYTHING at all distrubedme, if i caught myself even for 0.5sec thinking of something different then POTTINg the ball (maybe other englisch, maybe other speed, anything) i HAVE to stand up, chalk up, and get down
8/ DONT count the amount of balls ive potted or the amount of balls needed to run out. it DOESNT matter.
9/ dont get my eyes of the cb for 1sec to check where my cb should be after position (dont know yet how to not do it, cuz im still missing so much balls just because me eyes move away for a short time to check on position)
you are NOTHING with good position and no pot. u are ALL with a pot and bad position. u can still play save, or change your plans after. Dont be afraid of not sticking to your original plan. play what the table gives u, not want u want yourself to give.
10/ if after x shots your position is getting slightly out of hand. play the next shot at 200% concentration to get into perfect position. 1 inch to far after one shots, becomes 3" after 2shots (cuz u got another angle then u wanted) that gets 6 " after 3 shots etc...

mmm could go on for hours. no idea of some are usefull but they are to me, and thats what matters. if doing 250 situps works for u, do it. if it dont. dont waste time on doing it.
11/ i like to play as a underdog. if i lose. thats what i'd espect. if i win, greath pleasure. this way im always happy of the outcome. and if u are happy, u are enjoying the game. if u get upset cuz u are losing vs a worse player. ull lose your focus.
12/ play each frame like if u where 9-10 down and first to 11. no room for errors, no room for heroic pots.