I use a mityvac to bleed my brakes, but if you don't have one it's still very easy. The main idea is to use the pedal (or lever) to push the fluid through the master cylinder, brake line and
caliper. Pump the pedal (or lever) and hold. Open the bleeder valve. Push the pedal down to the stop with the bleeder open and do not let up on the pedal until the bleeder is closed. If you let up on the pedal with the bleeder open it will suck air back in the system and your pedal will be "spongy". Repeat until all of the air (bubbles) is out of the system and the pedal is very firm. You can reduce the mess by installing a clear piece of tubing on the bleeder nipple. Use clear so you can watch for bubbles. If your pedal is spongy you did something wrong and take your bike to the dealer. You don't want to mess around with the brakes.
What Ducmeat said with one addition - if you have an older Monster with the brake under the swingarm, you may need to take the caliper off and put it above the swingarm when you're bleeding it, to get all the air out. I thought my master was screwed until I did that, as the lever just wouldn't "tighten" up. Major props to Ducatisuite!