When running classes, you need to adjust your teaching style and techniques for your students.  Over time, you will encounter many different students, each with their own unique learning styles.  Identifying learning stayles is your first challenge, pay close attention to your class and read their body language.

An old rule of thumb I use is 4 hours of preparation time for each hour of class time - especially the first time around.  Actually, I put in far more effort than this.  Once you have developed your material, the next time around goes much faster.  Many novice instructors try to "wing it".  Although this saves time, you will overlook crucial class material and generally take much longer in class than had you prepared properly (and be a nervous wreck as well).  Formal classes may require prepared PowerPoint presentations.  Even purely outdoor classes should have a checklist prepared.  I laminate my checklist and refer to it often during breaks.  Give strong consideration to providing some sort of hand-out at the end of your class - your students will really appreciate this.

Effective feedback is a crucial part of coaching/teaching.  Pay close attention to how your students are mastering the skills you have taught them.  Look for any dangerous or bad habits and nip early.  The new ACA assessment program is a great way to gain experience in feedback skills.