First let me say I agree with everyone above, and the next thing is ...I'm not surprised how many times do you see people that are completely off balance and finally I can't take it anymore and tell them"uuhh your crooked,off balance" and they always say"oh am I?" and I just think how do you NOT feel that!
I used to be one of those people. That was back when I went to horse camp once a year, and that was it. I had absolutely no feel. None. Being off balance was what I was used to, and so it felt right
to me. I didn't notice that I was practically on the side of the horse.
I can clearly remember when I first started taking lessons on an every-other-week basis. My instructor told me I was balanced correctly, and I remember thinking about how WEIRD it felt. There was this little voice in my head saying "this feels wrong".
My next instructor would tell me every time I got off balance. This helped tremendously. Suddenly, I started to tell when I was off balance, and be able to correct myself.
Personally, I think that time is what it takes. Lots of time in practice in the saddle, preferably on a consistent basis.
I also think that you need to be able to get to know a horse at least somewhat. Up until I started riding at the barn I'm at now, I was put on a different horse nearly every week. When you're doing that, it's hard to develop a feel, as going from one horse to another often feels very different.
Now that I lease, I can tell so much more about the horse I ride- Skippy. I can tell when he's nervous, excited, lazy, feisty, listening to me or somewhere else entirely- and more. I can tell if he's on the wrong lead, and I'm slowly getting to be able to tell if he's on the right diagonal or not.
But, I'm not at the point where I can move his hooves exactly where I want them. Nor do I want to be. Skippy is a relatively old horse, and most of the time, he knows what he's doing. There are times where I get nervous, but put my trust in him, and he's never failed me. Lately, I've found he doesn't spook as automatically as he used to- it's hard to explain, but it's as if he's saying, "Okay, now you take care of me. Should I be scared?"