Interpersonal skills can be challenging for some. As an instructor, you will need to lead and leaders are not always the most popular in a group. Every class has new characters and you will always need to adapt to the needs of your students. Solid preparation will help a great deal as it will boost your confidence and that will certainly help command respect/attention from your students. You will need to be somewhat flexible.
People learn at different rates and in many different ways. Some students will certainly surprise you. One of the neat aspects in our classes is the students in general have chosen to take your class. You will often have a wide variety of backgrounds. Some students may know more about certain topics than yourself. A great example is first aid topics - I have often had doctors, nurses, and EMTs in my class. Perhaps they can co-teach something within their expertise or help in some other manner. It is a real bonus when the instructor learns a new trick or two. Others may need a bit more of a challenge to maintain their interest.
Communication, especially careful listening are skills you will need to constantly work on. Avoid the common problem of focusing on one or two star pupils and losing the remainder of the class. I have heard of numerous otherwise excellent teachers that make this mistake. I like to pelt my students with follow-up questions and carefully spread them around. I often look for the shy students as well. They feel nervous at first but quickly gain confidence when they succeed. When talking, try to spread the eye contact around the class.
We talked about feedback in a separate article. If someone pleasantly surprises you in mastering a specific skill, compliment them and be specific if possible. It isn't always easy but maintain a cheerful outlook - this can be infectious.
One of my favorite teaching topics is judgment. The ACA "Challenge by Choice" motto is a really good one for our sport. I really stress that everyone needs to be responsible for their own decisions. I teach youngsters that it is OK to walk a rapid even if older persons (even dad) is overly encouraging. Running rapids when you are petrified is a losing proposition and simply is not fun (or safe).
When paddling more advanced rapids, there are many more choices each paddler can take. Some paddlers are masters at identifying sneak routes. Others seem to choose the most difficult line imaginable. We are all wired differently. Resist the temptation to say one way or another is wrong. It doesn't hurt to ask why they ran a rapid in a different manner than yourself. Perhaps they needed a different type of challenge or perhaps they might have noticed something you missed like that stick several inches below the surface of the water.
You will often find classes are a team effort and your students will help in many different ways. I have been bombarded by rain and the students constructed a tent city. I was sick to the gills the first day of one class and my trained assistants carried on for me while I watched and made minor assists. A great co-teacher inured himself in the parking lot right at the beginning of a class. This became a neat teachable moment on the value of a decent first aid kit and the need for first aid training. I have had many other surprises as well. You will need to be very adaptable, creative, and have alternate plans ready just in case.
As a club teacher, I am really fortunate that I can recruit a large number of excellent helpers with numerous skill sets. They often provide one-on-one training when necessary or excellent expert training on various topics. We had two lifeguards in a SWR class which I used for C Spine practice rescues and panicked swimmer rescue drills. We had a blast with those exercises and the students learned a great deal.
Site selection is also crucial. In my area, all the local schools use Anglers Inn. In many ways, it is excellent for beginner kayak classes - perfect difficulty level, lots of flatwater, etc. It also happens to be quite crowded. Teaching there can be a major challenge - who is in my class for instance. That location has far too many distractions for my tastes. Instead, I teach at the Lock 5 Feeder Canal. This also has the right level of difficulty and I typically have the whole place to myself - no competition. When it is hot, I gather students in the shade so they are not squinting or over-heating. Natural coves are great for consolidating students together. Give yourself every opportunity to succeed. Here is a nice article on this important subject: Interpersonal Skills.