Step 1: Get the bike ready
1: Open pressure release if your bike has one. This will make it easier to kick over and less likely to kick the pedal back at you. This could either be located as a small lever on the handlebars or on the engine somewhere.
2: Turn on the key. This is pretty self-explainatory.
3: If you're starting a scooter, put it on the center stand and hold the brake. Many scooters won't start without a brake being held down.
4: Put on shoes. While not an absolute requirement, flip-flops, heels, and bare-feet don't tend to get along well with kick starting motorbikes. I've personally gotten stone bruises from kick starting a quad in flip-flops before. You should have decent shoes on if you're going to be riding a two-wheeled vehicle of any sort anyway.
Step 2: Kick the thing
If you find yourself kicking 'til you're blue in the face you might have another problem and need to refer to this fine instructable.