Setting up a good online lesson is pretty easy. Here are some tops tips to make them work really well:
1) There are some great online textbooks which are not expensive. The best ones are probably the CGP revision guides and textbooks. You buy the hard copy and get the online version free. Both tutor and student will be able to see the work easily.
2) It is best if the student wears a headset. Most teenagers have these for gaming, and these will be perfect.
3) For maths, it is really helpful for the tutor to see exactly what the student is writing. This is best done with a tablet and pen. Wacom has a really good version for just under £40
4) There may be internet glitches and times when the tutor and student are out of touch, unintentionally, during the lesson. This is not a problem as long as the student has work to be getting on with-this can be set up early in the lesson/tutoring arrangement.