Clues to choosing Preterit or Imperfect
What are some words in Spanish that help to clue you in on whether to use the preterit or imperfect. Isn't "de repente" usually a clue that you should use the preterit?
2 Answers
And here's some phrases that often are associated with the imperfect tense - you'll find them here in this article from Study Spanish: 
a menudo often
a veces sometimes
cada día every day
cada año every year
con frecuencia frequently
de vez en cuando from time to time
en aquella época at that time
frecuentemente frequently
generalmente usually
muchas veces many times
mucho a lot
nunca never
por un rato for awhile
siempre always
tantas veces so many times
todas las semanas every week
todos los días every day
todo el tiempo all the time
varias veces several times
Here's some flash cards with just what you're looking for
Common words found with the preterite
And you'll find the following list at Study Spanish
ayer (yesterday)
anteayer (the day before yesterday)
anoche (last night)
desde el primer momento (from the first moment)
durante dos siglos (for two centuries)
el otro día (the other day)
en ese momento (at that moment)
entonces (then)
esta mañana (this morning)
esta tarde (this afternoon)
la semana pasada (last week)
el mes pasado (last month)
el año pasado (last year)
hace dos días, años (two days, years ago)
ayer por la mañana (yesterday morning)
ayer por la tarde (yesterday afternoon)
