Does anyone have a foolproof routine or rule book that has changed bad sleepers into good sleepers?

[permaquandry]

Just that really. Having a bit of a time getting my 5 yr old and 9 yr old to sleep 5 yr old has always been pretty easy, 9 yr old always been terrible but prior to this hot weather had been getting better.

The heat has made it particularly bad lately for both of them but I could do with some advice to follow to the letter to get back to a decent bedtime that doesn't take up the best part of 3 hours.

Btw, have done a lot of the suggested things, no telly, no devices after 5ish, relaxing reading/no reading before bed, getting up early, doing things all at a set time etc. I just feel I need to follow a program, particularly with the holidays coming up.

Thanks.