How to Tell the Difference Between the Imperfect and Preterit in Spanish
Step1
First of all, know what it is you wish to say in the past tense, whether you want a completed action in the past or whether you want to describe an action or weather status going on in the past.
Step2
Line up your verbs in -AR, -ER, or -IR and determine the past action as in the first step. If you wish to say : " I spoke in Spanish" or: " I was speaking Spanish", or: "I used to speak Spanish"
Step3
In the case of : " I spoke Spanish", know that HABLAR is an -AR verb, its conjugation goes: hable', hablaste, hablo', hablamos,hablaron.
In the case of: " I was speaking Spanish", again taking the -AR verb, HABLAR, its conjugation now goes: hablaba, hablabas, hablaba, habla'mos, hablaban. Big difference between -AR verbs for both tenses.
Step4
In the case of certain verbs already mentioned as in -ER and -IR verbs as in TENER(to hold), Preterit forms conjugate(note the irregular forms): tuve(irregular here), tuviste, tuvo, tuvimos, tuvieron--endings reflect -e, -iste,-o, -imos, -ieron. For Imperfect forms: teni'a,
teni'as, teni'a, teni'amos, teni'an, with the translations "would", -ing ending, 'used to".