Use the auto-focus camera mode since bubbles are short-lived and adjust to blur the background for making the bubble stand out. Keep the shutter speed high and camera stable to freeze the shot.
If one is to do out-door bubble photography, still early mornings are generally the best to shoot. The low morning sun gives nice light to illuminate the bubble.
Always be persistent and patient for bubble photography. Look for the calmest of conditions and keep trying, experimenting to be eventually able to get some good shots.