There are two common methods for flossing - the "spool" method and the "loop" method.
The loop method is often effective for children (or adults with dexterity problems like arthritis). The loop method works like this: Break off about 18 inches of floss and form it into a circle. Tie it securely with two or three knots. Place all of your fingers, except the thumb, within the loop. Use your index fingers to guide the floss through your lower teeth, and use your thumbs to guide the floss through the upper teeth, going below the gum line and forming a "C" on the side of the tooth.
The spool method is the most popular for those who don't have problems with stiff joints or fingers. The spool method works like this: Break off about 18 inches of floss and wind most of it around your middle finger. Wind the rest of the floss similarly around the middle finger of your other hand. This finger takes up the floss as it becomes soiled or frayed. Move the floss between your teeth with your index fingers and thumbs. Maneuver the floss up and down several times forming a "C" shape around the tooth. While doing this, make sure you go below the gum line, where bacteria are known to collect heavily. th either method of flossing, never "snap" the floss because this can cut your gums. Make sure that you gently scrape the side of each tooth with the floss.
Gums may be tender or even bleed the first few times after flossing - a condition that generally heals within a few days.