Wow, good responses. I just have a couple of additional thoughts:
Corners:
Manny is right, braking into a corner is often not the fastest way around the corner. You have those knobs on the sides of your tires for a reason, so don't be afraid to lean that bike into a sweeper and drive around the corner. Also, DO NOT look at the corner. Look at where you want to go AFTER you exit the corner. Too often, folks will be so focused on the corner, they watch their front wheel as they go around the corner, which will only slow you down. The only time I brake into a corner is if it is a really tight short corner that does not allow driving through the corner. In these cases, I power hard from corner to corner to help compensate for the lost momentum caused by braking.
Jumps:
On a 125, you pin the bike, and keep shifting. On a 250, just stop shifting a little sooner, and don't keep it quite as pinned. However, on a 500, I jump a gear high to avoid wrapping the motor up like a 125 or 250. I have found that the bike is much easier to control in air and on landing with lower RPM's at liftoff, and much easier to straighten out if I leave the jump wrong.
Manny also has it right on with the practice. Don't start too big, as you might end up taking time off while you heal...
Have fun.
Rick