Fig. 'Dead Swimmer' to 'Streamlined'
One of my favourite swimming drills across all levels of swimmer. Back to teaching after 18 months (or is it two years). Loaded on a Kindle I show it to swimmers in the water and walk them through it. We repeat it in the deep end of the pool and later build in gliding and kicking drills.
Of course, every kind of drill and programme can be found on YouTube.