You should brake BEFORE the turn in point. I f you get too hot
into a turn, don't brake, or you'll open up the trajectory and end
up going wide. Force your eyes on the apex, and lean the bike
(don't forget to get out of the bike, or you'll scrape all kinds of
bits until you fall).
Of course, GP riders and other professional racing pilots will stay
on the brakes for longer, so let's say you throw that argument at
me. Well, they hang on to them further, but they are easying the
pressure on the lever, not doing the braking there.
Let's see if I can explain that easily by steps (procedure for
track riding/racing):
1) Full gas down a straight
2) Approaching corner, start braking gradually, but firmly (like
it's usually said for triggers of guns, don't pull the lever,
squeeze it!).
3) As you brake, downshift, blipping the throttle. Should the rear
wheel start jumping from a harsh downshift, press HALF of the
clutch, and it will go steady again.
4) As you approach the turn in point, gradually release the lever,
adjusting the speed of release to how fast you want to go into the
turn.
5) Go into the corner in the gear that will allow you to EXIT it
around 8,000-9,000, where max torque is for our bikes. That's why
we have free practices, to sort out the gearing and stuff
6) You can tell that you were going fast if you feel you came in
too hot, but at the apex you could accelerate again. If you
accelerate easily before the apex, you can still go in faster. If
you barely made it past the apex and opened the trajectory, then
get in slower, cos you're loosing out on the exit of the turn.