Do not teach...
Part of developing your own skills is found in teaching, but you shouldn't teach...
While that seems a contradiction in terms, let me explain what I mean. A teacher is often viewed as someone who imparts knowledge to others so they may copy it. While there is some benefit in that method, it does not serve well in martial arts - especially in ninjutsu.
If we look at the term 'sensei' it is often translated as teacher, but its actual definition is 'one who has gone before'. The idea contained in this is the person in front of the class has experienced the skills they are teaching and can offer insights to the principles involved. This doesn't happen overnight. Through the act of explaining techniques, answering the 'what if' questions and being honest and open to insights, the person teaching develops a deeper understanding of the art. This means that a simple technique taught five years before, over time, will have more meaning and application in it. Hatsumi sensei has often said that only by learning the kihon (basics) can the formless be understood and applied.
To be a sensei in ninjutsu is to have an obligation to those who wish to learn. To have a sense of duty to not only pass on accurate information, but to also empower the student to be able to see principles and work out how they may be applied to different circumstances. The end goal is to have the students develop their own deep understanding and be able to then pass it on to others. This layering of understanding should lead to the art as a whole being enriched.
Every time when demonstrating a technique there is an opportunity for the instructor to gain new insights into the principles in the technique. Using different uke enhances this as there has to be adaptability to different students height, weight, flexibility and familiarity with the technique. Hatsumi sensei in the past has said that he does not show the same technique twice, as uke cannot attack exactly the same way twice. This can be seen when, after the first demonstration, uke begins to anticipate the technique and changes intent, resistance or distancing. Instead of becoming frustrated with uke, this is an opportunity for the instructor to find the subtleties in the technique that allow them to achieve a similar result.
It should not be a quick or lightly considered decision to teach. The person who is now teaching has an obligation to anyone who is taken on as a student. There needs to be a commitment from the sensei that is equal to, if not more than, that of the student.
The commitment to keep learning, keep studying, to develop understanding when showing techniques. To find a way to communicate these ideas to the student in a way that they understand. Whether you rent a space per hour, full time or teach in the garden you need this mindset to best serve those that entrust you to help them understand the art.