Trainers should decide, in advance of training the behavior, what will and will not be reinforced. If the trainer waits until the behavior occurs before deciding, the click will be invariably late and inconsistent. The animal must get something it wants or needs. The trainer must get behavior or some other satisfaction out of training. Reinforce often, especially early in training.
Ratios are overused and often improperly used.
It is not mandatory to use ratios while shaping. Properly used continuous reinforcement, plus fluency training, give moderately strong and very precise behavior. Reserve ratios for highly repetitive, long duration or other special behaviors.