tener
Yo tuve cumpleaños ayer (preterite is used since it's something which is completed)
Isabel tuvo un gato toda su juventud (preterite is used for actions that happened in a period of time)
Vosotros teníais muchos problemas con el coche antes (imperfecto is used when we don't know if something has already ended)
hacer
Tu hacías siempre buena comida
Tu y yo __ muchas tonterías (the sentence doesn't give you any indication as to the type of verb which should be used)
En su epoca Juan, Pedro y María hacían el mundo mejor ( something that happened but cannot be seen as ended)
comprar
Pepe siempre compraba cerveza ( something that repeats itself)
Amanda y tu comprasteis helado la semana pasada ( la semana pasada indicates we have to use preterite)
El fontanero compró un nuevo coche antes de ayer ( antes de ayer indicates something which has ended)
Hope this helps. I may be totally wrong of course. If some native speaker could check this, he/she would do a great favour.