Help with Preterite/Imperfect

I'm having trouble grasping the difference between the preterite and imperfect. Can someone look at the paragraph I paste here and tell me what each number is, preterite or imperfect, and why?

• Cuando era niña, siempre (1) (ir) a la escuela caminando, pero ese día (2) (ir) en autobús. Yo no (3) (ser) muy buena estudiante, pero me (4) (gustar) mucho ir a la escuela. Ahí, mis amigos y yo (5) (jugar) en nuestros ratos libres. Esa mañana, cuando yo (6) (llegar) al salón de clases, (7) (oír) al profesor y a mis compañeros hablando muy bajito (low). Todos (8) (estar) esperándome. Ellos me (9) (cantar) el Cumpleaños feliz y me (10) (dar) muchos regalos. ¡Fue un día inolvidable!

I could really use some help here.

Welcome to the forums!

Please give this your best try first.

(If this is your homework, you should have selected the 'Practice & Homework' forum for posting. Let me know if you want the thread moved.)

In brief, preterit is used for past actions that have been completed while imperfect is used for past actions that were done in an indefinite amount of time or continuously.