I'm writing a primer on music theory, and I have this same fear. I resolve it in three ways:
1) I try to make the writing entertaining enough that people won't mind reading something they already know
2) I added an anchor tag saying "click if you already know this stuff"
3) I added tooltips explaining vocabulary words, so if you skipped a section and end up not knowing everything you thought you did, you can use the tooltips to refresh your memory.
These three factors I think combine in a really nice way. I'm excited to post it here when I'm done with it.
1) I try to make the writing entertaining enough that people won't mind reading something they already know
2) I added an anchor tag saying "click if you already know this stuff"
3) I added tooltips explaining vocabulary words, so if you skipped a section and end up not knowing everything you thought you did, you can use the tooltips to refresh your memory.
These three factors I think combine in a really nice way. I'm excited to post it here when I'm done with it.