Reddit reviews Swimming and Water Safety

The basic class structure I use for swimming lessons is:

Warm-up - gets the wiggles out, sets up consitency
Review - go over things they know, still correct technique
Introduce - introduce new skills that build on the known skills (this varies on age group, skill level and difficulty of what is being taught)
Review - go over new skill, combine it with previous skills
Cooldown - something fun, game, etc to let them know class is over / reward them for being awesome earlier

Grab this and this, though both only have basic diving material in them, it'll be an excellent place to start with non-divers that you can build off.