99% of people in the UK learn to drive on a manual car, mainly because if you pass the test on an auto, you're only ever allowed to drive an auto. In fact, automatic gearboxes - except on large executive cars - have never been very popular over here, even when sold for no price premium. It's a perceived "control" thing.
The main thing to remember is that you don't have to let the clutch all the way out, all at once. I used to stall the car constantly before the instructor explained this to me. The second thing, most important for hill starts, is to allow the car to "sit up" on its suspension before you release the handbrake.
In terms of good practice, NEVER use the clutch and throttle to hold the car on hills, put the gearbox into neutral and take your foot off the clutch when waiting for more than a couple of seconds at lights, and learn to use the "dead pedal" (footrest) when not changing gear, rather than riding the clutch. You know all this but she doesn't.
As for double-declutching when changing down...well, it's just for show on a modern car, although the weak synchro on an NA gearbox means it occasionally helps you go from 2nd to 1st when the gear oil is cold.