Let the donor control the rate of ascent. Be ready to switch to an emergency ascent if necessary. While ascending, remember not to hold your breath. Exhale slowly at all times when you don't have the regulator. Holding your breath while ascending can lead to an air embolism.
Buddy breathing can be stressful even under normal conditions.
Practice in a pool until you've mastered the technique. Accept that the dive is over, and head for the surface. Make sure you are an officially certified scuba diver before entering the water. Scuba diving is an inherently dangerous activity that can result in serious injury or death. We recommend that you seek proper training and equipment before attempting this activity.