Find out what your students' musical interests are before you begin. It's important that you know what they expect from you as a teacher and what their goals are. Knowing what type of music interests them will help you tailor your lessons.
Familiarize your students with their instrument. Teach the open strings on the guitar and explain how each fret represents a half step up on the musical scale. Teach him a C major scale and show him how to play it forward and backward. Explain how playing the scale will help get him familiar with the neck of the guitar and how it will help strengthen his fingers.
Introduce the C major and A minor chords during the next lesson. These are simple chords used as the basis for many songs. The idea is to introduce chords at each lesson since chords are the quickest way to get your students to play a song. Chords also sound more musical than playing scales, which will typically keep student interest longer. Have your student play the C major scale for you and determine how well he has mastered it before you introduce another scale.
Teach right- and left-hand playing at the same time. This means you will show your student how to strum and vary the rhythm of the strums while having him make chords and play scales. If you teach these things separately, it's almost impossible to get your student to work them together later on.
Continue to teach major and minor scales at successive lessons, explaining how the patterns remain the same and only the notes change depending upon the key (starting note) of the scale. Add a couple more simple chords. A major and E minor are good choices. You want to teach theory without being obvious, and the continual introduction of chords
Teach a simple strumming song by the third or fourth lesson. Many songs can be played simply with just chords. Your student won't be playing solos yet, but he will be able to recognize the songs he plays. Don't try to rush note reading. For guitar players, consider teaching the tablature method of reading and writing music. Tablature is a type of musical notation specific to the guitar using a six-line grid representing the strings on the guitar with numbers written on the lines to represent which frets to play. This is often the best method to get students playing songs more quickly in the beginning.
Encourage your students to work on their ear by trying to play along with their favorite songs. Trying to locate the sound they hear on the guitar is a great way to familiarize them with finding the same sounds in different locations on the guitar.