What is the difference between preterite and imperfect.

Preterite- Something that has been completed. Has a definite beginning and ending.

Ex) Fui al baile anoche. I went to the dance last night.

Phrases that trigger preterite:

Imperfecto- This is something that never really ended, is still going, or has been repeated. Is also used to tell age, time, emotional status, what people were doing when something occurred, and weather

I know it's really hard to remember when to use which one. Imperfect was the death of me in Spanish class.