1) Keep things fun. In my opinion, this is the most important thing to remember about teaching, and it's the thing that took me the longest to learn. If your student loves blues, don't spend the entire lesson focusing on classical music. If your student simply wants to learn how to strum some chords, don't spend your time learning heavy metal solos. Listening to your students and understanding what they are wanting to learn will help keep the lessons fun for them. This will help keep your students motivated to continue learning their instrument and also hopefully keep them coming back to lessons.
2) Use a book (or two). There are many excellent guitar teaching books available that help provide additional structure for a guitar lesson. I'm a fan of using the Hal Leonard Guitar Method Book 1 for beginners. After that, there are countless options of books that were written by very professionals for us to increase our musical knowledge. Generally, I like to spend roughly 1/3 or 1/2 of the lesson in a book. The rest of the lesson can be spent learning other songs or theory that the student may be interested in.
3) Bring a laptop and printer. Bringing a laptop and printer to lessons allows a teacher to immediately print out songs that a student is interested in. This saves time and let you jump right into a song that is on their mind. Remember to edit and save your charts for future lessons!
4) Don't be afraid to ask for your payment. It is human nature to forget things. We all do it sometimes, and it isn't rude to remind people if they accidentally forget to pay. In fact, I've found that most people appreciate you reminding them for your payment, as it's one less thing they have to always worry about.