Well equiped, preferably run by professional full time instructors not mixing Krav Maga with Martial Arts. the mentality of the students should be humble, polite.
NOT: with a Rambo type macho mentality
Professional, well educated and humble.
NOT: showing off, with a Rambo type macho mentality
The problem is that a lot of Krav Maga Instructors are in fact Fitness Intructors or Martial Arts Sensei with some knowledge of Krav Maga.
Krav Maga is a simple system based on concepts and priciples. It doesn't look fancy, Krav Maga is brutal.
Your training should involve some kind of sparring.
Training partners should touch eachother! There has to be physical contact. Training without is useless. Forget about the muscle memory shit they tell you. This is the fact: you need to touch your trainingpartner and you need to be touched (hard) in order to get used to contact!
NOT: fancy moves, 400 techniques, 15 exams, kata's, japanese terminology, rituals.
Remember, Krav Maga is not about the instructor but about the system. To be a Master it takes Indesign, Photoshop, a printer and some marketing skills.
To be a good Instructor takes a bit more than that. He has to know the principles of Krav Maga. He has to know about Anatomy, Fysiology, First Aid, Gun, Knife and Stick handling, Psychology and so on. He doesn't have to be an Athlete.