Yes, always warm a two-stroke engine before riding ( I'm assuming you have a two-stroke? ;) ), or you run a risk of seizing the piston and/or crank. Simply let it idle, giving it small blips of throttle to keep it from loading up, until the cylinder and radiators feel warm. It usually takes two or three minutes for my bike.
I warm mine up with the choke on for 15 seconds at idle speed, then i turn the choke off and blip the throttle for 45 seconds. I ride the bike easily, low revs, no powershifting or cracking the throttle for a few minutes. Once the bike has been running about 3 minutes the motor will be warm and ready to take a beating.