Set up an hourly or half-hour fee from the outset, explaining your base rate to your students and telling them in advance about your cancellation policy for lessons.
Write the information down on a piece of paper and have them sign or initial it to show they understand the agreement.
Set up a scheduled appointment with each of your students, typically for an hour or two hours of lesson time.
Plan your lessons well in advance, ensuring that you have enough material to fill the allotted time and that the material is tailored to the student's skill level. For example, don't try to teach a beginning student advanced programming skills if they are unable to open a document in Word, and vice versa.
Keep attendance records for your students, presenting them with weekly or monthly bills for your services.