Threadless headsets are easy to adjust and work on the same basic principle. The bearing races need to press against the bearings. The bolt in the top cap will put pressure on the stem, which presses on washers, which press on the races, which press against the bearings.
Remove center adjusting bolt and cap. Inspect steering column length. The steering column should be recessed inside of the stem. Lubricate adjusting bolt and re-install cap and bolt by hand only. Do not over-tighten!
Loosen stem bolt(s) that secure the stem to the steering column. Lubricate these bolts if they are dry. NOTE: DO NOT LUBRICATE INSIDE STEM/STEERING COLUMN SURFACE. Wiggle the stem side to side to see that it is loose. If the stem is jammed or frozen to the steering column, no adjustment can be made.
Align stem straight, and gently secure the top bolt. Stop just when you feel the cap bump the stem. Secure stem bolts. Check for play by pulling back and forth on the fork. A knocking sensation is called play. Turn the handlebars in different directions while checking for play. There should be some minor play at this early setting.
LOOSEN STEM BOLT(S). Turn adjusting bolt in center cap only 1/8th turn clockwise. Secure stem bolts, check for play again. Repeat until play disappears. Remember to loosen stem bolts before turning adjusting bolt.
Align stem and secure stem bolts fully. Do not over tighten stem bolts. Consult your bike shop for proper torque. Here are some broad guidelines: If you have 2 stem bolts, secure to 70 inch-pounds each. If you have one bolt, secure to 120 inch-pounds.