0. concept of "where is your lighting source going to come from"
1. manual flash vs TTL flash(and all newfangled electronic variants)
2. based on 18%grey reflectivity, => guide number = numerical value of aperture x distance from foreground subject
3. fill-in flash vs "full-power flash" vs ambient exposure vs long exposure
4. concept of exposure compensation
5. concept of flash-exposure compensation
6. leaftype shutter vs vertical FP shutter => concept of x-sync speed, concept of electronic high-speed flash
7. motion effects: concept of slow-sync flash , rear-sync flash, front-sync flash
8. stroboscopic flash
9.macro: concept of macro flash
10. concept of "painting with light" (tedious technique)
11.extra effects: filters and flash, colour temperature, compensation
12 related topic: reciprocity and film behaviour: "1x1000 is not the same as 1000x1"
While general flash techniques is good to learn, for myself found its better to concentrate on how the build in flash / flash modes can/cannot help me seems a better idea ( no hotshoe....no choice....)