A bit late I know but as chappers said find you and your bikes performance parameters, especially the front brake. It's always worth finding a quite piece of road or a supermarket car park to practice.

Start from a slow speed and build up. Don't just grab a handfull of brake though, it's more about applying the brake swiftly and smoothly until you find the point at which the wheel is about to lock. That will take trial and error though and each bike is different. You're bound to lock the wheel when you first start so be ready to release the brake swiftly when you do or you'll be off again.

Once you've got your optimum braking pressure sorted so it's more feel than thinking about it. Start to build up your speed a bit at a time and don't do anything you're not comfortable with. Eventually you should be able to brake and stop quickly from quite a high speed.

Once you've mastered that then you want to do the same thing on a wet day, but remember there will be less grip so the wheel will lock much more readily.

The point is you're getting the 'feel' for the brakes and amount of grip you have. Then when you have to do it for real you'll stand a much better chance of stopping. Of course the real secret is not getting into the position of needing to stop that fast in the first place, but there will always be times when you need too no matter how good you get at reading other road users, surfaces, conditions, etc.

Practice makes perfect as they say...