Most important things to look at
1. Instructor who has been around a bit so has the experience of loads of different situations. So someone who has instructed for 500 plus hours, has loads of time on the machine you are going to learn in. Has done utility work in a machine as well as pax carriage. Ex military guys make good instructors as they will have seen and done most things plus they will have been through a rigorous selection process so will be very good stick men.
2. Keep the same instructor for the whole time
3. Somewhere where the weather is changeable so you experience mother nature, no good flying in blue skies every day
4. Type of helicopter where instructor WILL do engine off landings, run on landings with pedals stuck at nearly full deflection
5. In an area where you can fly where there are open spaces for better continuation training without too much civilisation and controlled airspace
Most important do you get on with your instructor as you are really a team, if the team doesn't work ...............
Good luck