This link has lots of exercises on tenses including these ones:
some interesting things to watch / do regarding the “prétérit simple VS prétérit BE+Ving ” new sequence.
some old-school grammar taught live by an old-school (but very efficient!) English teacher : CHECK THIS OUT!
I used this nice animation for a short / easy listening comprehsion with prétérit BE+Ving verbs.
YESTERDAY AT THE BEACH : a nice animation + RAGS TO RICHES game! >>> GO !