Cuando me puse de pie de la silla , el vaso cayó. Cuando tuve que ir a allí, tuviste que ir a allí. (Si quieres decir que las dos acciones pasaron al mismo debes de usar "tuviste")

All senteces are right! the difference is liked to the conjugation and the intention of using each Tense. In your examples you have 2 verbs (parar= stand up and caer=fall down)---(please notice that "pararse and ponerse de pie" are the same) 1. Cuando me puse de pie de la silla , el vaso cayó. Preteritum , Preteritum t (Basically, at the time you stood up, the glass fell down) 2. Cuando me puse de pie de la silla , el vaso caía. Preteritum, imperfect past or progresive ( at the time you stood up, the glass was falling down) 3. Cuando me ponía de pie de la silla , el vaso cayó. imperfect past, preteritum ( when you was standing up, the glass fell down) 4. Cuando me ponía de pie de la silla , el vaso caía. Imperfect past, imperfect past (When you was standing up, the glass was falling down) Usually imperfect past needs to be followed by " something more", is like telling a story like.....the sentence Number 3 is a good example of that