Preterite/Imperfect Spanish help!?

i am having a hard time distinguishing when to use preterite or imperfect. I know you use imperfect for an on going past and preterite is when something like one event happened. Would a sentence like "Juanito se despierta temprano" would the despertarse be Preterite or Imperfect? Also another sentence "Parece que esta muy cansadio". Would the Parece be imperfect or past and why? i get some but something just don't make sense. thanks