It's very similar to golf. You start doing a little something wrong, and then you begin experimenting with this and that to see if it will help. Then pretty soon you're doing two things wrong.... Then you go to a golf pro and he straightens you out, until you start doing the next thing wrong. Even the greats like Jack Nicklaus or Tiger Woods have their own pros who can't play golf as well as Jack or Tiger, but who can see flaws neither of the players can see on their own.
It's really hard to know what mistake we're making, because whatever we're doing feels natural to us, since we repeat it again and again. People are lucky if they live near an archery pro who can watch them shoot and straighten them out. Not as many of them around as golf pros, unfortunately.
Since I don't have an archery pro I can drop in on, the best thing for me is to just make a game out of figuring out what it is I'm doing wrong. I know I can shoot well, because I've done it before. If I'm not shooting well, it's got to be one of three things: concentration, form, or equipment.
It's hard to focus on concentration if you're focusing on either of the other two, which is why people recommend focusing on the other two by shooting at a blind bale. You can watch your arrow flight or focus on your back tension without worrying about where the arrow is going to hit.
Then when you're out of ideas about form or equipment problems, it's time to focus on concentration, which means you shoot for accuracy and put all thoughts of form and equipment out of your mind.
Sometimes nothing works, but if you've had these slumps before and come out of them, you know something eventually will work. A lot of times I've picked up on some hint from this or another archery forum that has helped, because it's something I've forgotten or not thought of before.