Try to work on your core for riding. I grip the tank (not tightly) with my knees and keep a fairly loose grip on the bars.
As many have said, practice in a parking lot is a good thing. What I woul do is practice stopping from different speeds. Start out slow (stop from 10mph or 20mph) then gradually work up to faster speeds. No need to try to panic stop from those speeds. Get used to the natural dive of braking.
Also, and you'll hear differing opinions on this, I recommend using both brakes when stopping. most of your braking power will be concentrated in the front. When you grab a handful of brake, quickly, you'll dive faster. Concentrate on smooth, for the street. I'm not saying to not practice panic stops, just build up to them. You'll be able to feel, eventually, when your tire starts to lock up. That's different with each bike, so this is something even experienced riders do when they get on a different bike, so it's good practice to carry on in your riding career.
If your bike has ABS, you can grab the brake harder, without worrying about locking the front (in a straight line. Leaned over is different)
One of the best things about motorcycles is that the same physics apply to both a small and a big bike. The speed at which things occur is different, but what you learn on a 100cc bike will apply to a literbike. The point is you can learn a lot from a small bike, and do it at more managable speeds.
Also, and this is very, very important, look where you want to go. This is simple advice, but SOOO many people don't do it. What I mean by this is where you want to end up. If you go into a corner, don't look at the curb, or the houses, or the armco, look where you plan on exiting the turn.
If you have trouble with moving forward under braking, and need help gripping the tank, some skateboard grip tape or Stompgrip works wonders.
Good luck, ride safe
