I like to get students to start playing as soon as possible in order to get enjoyment from their lessons and practice, even if it is very simple at first! Having taught all ages and levels over many years, I tailor the lessons according to the aims of the pupil, for instance whether they are just learning for pleasure, or wish to prepare for examinations. If they are preparing for examinations, then part of the lesson can also involve sight-reading, aural training and theory, depending on their level.
I find it is a good idea for younger students to have a practice notebook, where one can write what they should work on while practicing for their next lesson, and which they can read to remember what was covered during the previous one. It is also good idea to get the student to start reading music as soon as possible, so they begin to coordinate between what they see, what they hear and what they play.
In general, each student will have different strengths and weaknesses, and focusing on the individual needs of the pupil is the most important aspect of the lesson.