One thing you can do, oddly enough, is to not worry about the bad days. It does you absolutely no good to worry about "bad days" and just adds another thing to stand in the way of keeping your focus on shooting good arrows.
"Bad days" is too vague of a thing to worry about, and offers you nothing you can work on to improve your shooting. If you have a bad day, and you will probably have many more of them, it's because you're doing something different than you were on the days when you shot well. Nobody other than maybe a personal coach can tell you what that is, and if you don't have the opportunity to be coached by someone, you just have to figure it out for yourself.
What you have to do is to develop good, solid, repeatable form. Study Terry's form clock, and try to match yourself to his allignment. It is hard to know when you're in good allignment, so maybe you can take pictures of yourself or someone can do that for you, and then compare your allignment with his. Get Masters of the Barebow 3, and learn what Rod Jenkins and others on that video have to say about drawing the bow, release, and followthrough. By all means, go to classes if you can. Study Masters of the Barebow IV 4 and learn to apply what they say about concentration and focus.
I've studied this long enough, and have done it right enough times now, that when some element of my allignment or form breaks down, it doesn't take me very long to identify what it is that I need to work on. But I remember earlier in my archery career when it was more of an accident if I did everything right than it was if I botched the shot. I would try and try to repeat those perfect shots, only to make the same or some combination of unknown errors again and again. Most of the time, whatever I thought might be causing the problem wasn't, and whatever I changed only made things worse.
However, eventually, through trial and error, I would stumble on something that would solve the problem, and I would shoot great for a while until I started doing some other thing wrong. Then it would take me a long time to identify that. The good thing is that when you identify a particular problem, like torqueing the bowstring, then you develop a body awareness of that particular problem, so when you start doing it again, you're able to correct it a lot quicker than you did the first time. But I don't know of any easy way to develop an awareness of all the multitude of allignment errors, execution errors, and focus errors that it's possible to make, other than just making them and then learning to identify them one by one.
Well, you could go back and be born with the genes of a Rick Welch or Tiger Woods, but I haven't figured out how to do that either.