If you - or a client has a specific problem with the external rotator cuffs then this may not apply so much - so test them to find out - or ask a physio or appropriately qualified person to do so. In my experience many common sports injuries follow the above pattern - external rotators dominating over the lone internal rotator - especially when you consider the deltoid muscle sitting over the top of the 'cuffs' is also an additional external rotator.
So, my top exercises for helping to fire up and strengthen the subscapularis, serratus anterior and fibres of lower traps (without getting too clinical and complicated with tubing or bands everywhere) are:
- Medicine ball push ups
- Bent over row
- Push up plus variations
- Dynamic hug
- Horizontal bar hang
- Prone cobra (Internal and external rotation of arm variations)
- Scapula retractions ala McGill
- Straight arm lat pulldowns