it takes a lot of faness...
For the longest time, I would clutch wheelies (in 2nd gear) sitting down and they wouldn't come up. It takes a lot of throttle control and clutch control to hit the right spot. If you redline it (in 2nd gear) and simply pop the clutch, you won't wheelie worth a crap. If you dont rev it enough, you won't wheelie worth a crap. If you are going too fast, even if you clutch it right, you won't wheelie worth a crap. If you are going too slow, you won't wheelie worth a crap.
I eventually found that around 40-50 mph, I could consistantly clutch perfect wheelies. After much practise, I can wheelie a wide variety of speeds now, but initially, I practised/learned at 45mph.
It also helps to slide your butt back til it hits the passenger seat.
Then after you get them up, you can work on your balance. Also, if you are ACCELLERATING, it is easier to wheelie, rather than riding a constant 45mph.
Now -- for the balance. If you clutch a wheelie, your bike is (for example) 45mph and 6000 rpms. (idk what it would actually be but w/e). So when you wheelie, your motor drops back down to 8-10k rpms and its easier to balance because your motor isn't tapping off the REV limiter.
If you power-on wheelie, or jump/bounce your front wheel up, 599cc bikes have to be STRUNG OUT, or 60 tooth geared, to accomplish this. So once you do it, you are in the redline range, and a small touch of the throttle will effect your balance a lot more --than if you were at a lower RPM.
Sitting vs. standing -- personal preference. That's about all I can say. Some people are more comfortable standing, it comes easier for them. Some people -- like me -- can't clutch as well while standing. While standing, you look through your windshield to see where you are going, while sitting, you look around the side of your bike --which at first will cause you to glide to the right.
Where is pink Gixxer dude when you need him? He's our resident stunter. Now he's got a green 636 like me...