As I've said before, the "trick" is to practice seeing how slowly you can make tight turns, not how quickly.
Remember that the tighter the turn, the faster the front wheel is rotating relative to the rear.
That's why slipping the clutch helps, or else you have to ride too fast to keep from lugging the engine.
It's almost pointless going into great detail, because while technique matters, everyone has their own individual comfort level, and there are more than one way to turn successfully. Some with good balance can perform slow tight turns at incredibly slow speeds, but more of us will rely on a bit of speed / momentum to stay upright.
General tips I have noted before:
Head turn. BIG head turn, like over your shoulder looking back to where you want the bike to go. This is not a natural turn of the neck / head for non-riding humanoids.
Clutch -- also known as the Friction Zone in the MSF BRC.
@Larry Fine and others call it "slipping the clutch", or "feathering the clutch." Call it what you will, but you MUST master control of the clutch and throttle. Steady on the throttle, and use the clutch alone to release the power to the rear wheel. YOU are in control of this, or should be.
Counterweight. Shift your weight to the outside of the turn. Some slide their butt over, some will not. Weighting the outside footpeg may also help.
Turn the handlebars. With proper control of clutch / throttle, you should be comfortable (or become comfortable) at full lock, even with a lean angle.
Moderate your speed with the clutch. This beast will NOT stand up by itself, especially with any lean angle, but a bit of momentum will prevent it from falling down. We all know how heavy this thing is.
As mentioned, a little rear brake action may help you as well. Lightly! Yeah, the front brakes will engage as well, but we're not using the front brake lever itself.
Don't try to stop with the handlebars turned -- it's almost a guaranteed gravitational encounter. Square the bars when stopping, or better, release the clutch and straighten the bike up; you can try over again if you mess up and miss the line or cones or cut-up tennis balls, or whatever you're using as boundaries.
Most riders will start with relatively large circles, and as they become more comfortable, they gradually tighten the turn until they succeed.
These are the principles, and while most riders can accomplish this if they want to, I rarely see big bike riders doing it exactly like someone else. Find what works for you, and keep practicing. It will be worth it.
