Basically, you can take the same approach as for teaching groups. You decide your objective for the lesson and plan how you will achieve it. Remember to have a variety of exercises. The same procedures apply of presenting language and practising it as well as error correction.The only difference will be the lack of group work; for any pairwok, you will need to participate. You’ll find yourself doing more of the work in a one-to-one lesson but as you get to know your student and build up rapport, this will balance out.
For the first lesson, you can get to know your student. Find out about his / her job and the reasons for learning English. Find out in what situations (s)he will use English (speaking, writing, reading). This will help you plan subsequent lessons. If the student has done a placement test to define his / her level, you can go over the test in the first lesson. If no test has been done, I suggest you do one to determine the level. Your school should have one available. However, do the test orally; it’s not a good idea to have the student writing away silently in the first lesson.
Finally, consider the seating from the beginning. Sit around a table with your student; sit close to him / her (not too close obviously!!). I say this because I once saw a one-to-one lesson with the teacher at the board and the student sitting at the back of the classroom.
Once you have met your student, you’ll have a better idea of needs and level. Feel free to write in at that point for more ideas.