There's a High Yo-Yo and a low Yo-Yo maneuver. High yo-yo is used most of the time to not overshoot, and a low yo-yo is used to pick up more speed. To do a High yo-yo pull up, roll over, and come back down. A low yo-yo is basiclly the opposite, roll over, pull up (since your already upside down it's more like a dive), roll over and pull up.
EDIT:
Now that I have some more time here's what my Flght Manual I have says.
High Yo-Yo
The High Yo-yo the root of all offensive air combat, replacing intelligent maneuvering for "G for Brains" high-G tactics. The high yo yo reduces AOT (Angle of tail, measures the angel between your flight path and that of your target) at the cost of increasing range between attacker and target. The yo yo begins during a turn fight when you have assumed an agressive position behind the bandit, but are stuck in a lag pursuit and unable to bring your nose to bear. Roll up slightly, maintaning the lag pursuit, then pull the nose up.
Low Yo-Yo
The low yo yo is the logical opposite of the high yo yo and performs the exact opposite function. Whereas the high yo yo decreases AOT and increases range, the low yo yo increases AOT while decreasing range.
The low yo yo is generally used when you have a good shot opportunity, but you're outside your weapon's maximum range. To get closer, you lower your nose below the horizon. Lowering the nose increases speed. Unfortunately, the increased speed almost always results in increased turn radius, forcing you into a lag pursuit and increasing AOT. A low yo yo, therefore, almost always requires a following high yo yo to correct the angles problem generated by the increased speed.
