It’s nearly impossible for me to pick just one!
A trainer needs to be a skilled communicator. This includes:
1) Good listening/input. For example, it benefits the client when you take in plenty of information from them initially to figure out where to start in their training plan. Getting feedback as you go is important, too. Active listening also helps you to deduce what kind of a learner your client is so that you can better work with them. Nonverbal language is key also. I’ve heard the figure that 87% of the way we communicate with one another is nonverbal.
2) Effective cuing/output. As stated, it’s important to know what kind of learner your client is so that you can get them to understand what you want them to do. An auditory learner might be able to take in almost everything you say. A visual learner is going to get the most out of seeing a demo of each exercise. A kinesthetic learner will understand a movement by actually doing it.
Communication output can also include non-verbals like smiling, high fives–all of the encouraging words and behaviors that come to many trainers very naturally 🙂 Most trainers are innately effective communicators, or “people people”, but it never hurts to think about how we can be better at it.
Trainers who are organized, reliable, and knowledgeable/professionally certified also benefit themselves and their clients.