Why? I think burn-outs are a wast of money IMO. The only time it might make sence to have a little fun doing one is when it's time to change rubber. But anyways just grap a handful of brake with your index and middle finger or all and just roll with the thumb and Don't let go of that brake. Keep your clutch covered for it's your safty if you feel the tire might catch.
I agree w/ jk6672 when it comes to a waist of money, but you'll figure that one out on your own.
Just stand up (relieving the weight from the bike),grab the front brake (however your comfortable), roll on the throttle (rpms will usually depend on the bike; your safe if you go w/ high ones), and let out on the clutch. If your worried about dumping the clutch, you don't have to. Just let out on it slowly, and you will feel the rear end elevate as the force starts to try and push forward. Keep letting out on the clutch and giving it power until the rear tire brakes traction. After that your can do what you like as long as you don't just let go of the brake. Also remember that if you let off of the rpms, there is a chance that your tire might regain traction. You don't want that!
You might want to try this on good, dry pavement so your front tire doesn't push/slip. Like everything else, this will take practice before you can try something new ie. rolling burnouts, etc.
Good luck! (w/ buying new tires)