The best advice I could give is become intimately familiar with the practical test standards for the rating or certificate you are trying to aquire. Find an instructor that understands this and you will have probably found a good instructor. This is probably one of the most overlooked training requirements in aviation. PT 61 and 141 each have their advantages. I liked Pt61 training due to intructors usually had different perspectives rather than the instructors at 141 programs that train at the school and turn around and instruct at the same place which can lead to tunnel vision in regards to training.