I have been a guitar instructor for nearly a quarter century.

I used to go under the name Mercury Guitar Studio, for those who might remember

Audio production

how to make a full mix

how to track your band

how to work with voices, and other instrumentalists

computer and DAW things

basic digital audio

advanced compression, reverb, etc.

Guitar 

classical

rock

reading and theory

school prep

summer whatnot

musicianship / band membership

note organization for gigging musicians.