I was struggling with learning the past tense verbs. The present tense conjugation would just pop into my head right away, no thought required. I still have to think about the proper past (preterit) tense conjugation. So, I know I need more practice and more drills.
I found two web pages to help drill the different conjugations into my head:
http://www.spaleon.com/index.phphttp://www.studyspanish.com/verbs/Hope the pages helps others.
Mike G.