I've found a LINK that will help you. 
> http://www.studyspanish.com/lessons/imp1.htm

But I also have one advice to you. You need more input that just trying to find a correct gramatical structure. Usually in Spanish, there are many phrases that are repeated everyday. Take a fiction/non-fiction book and just try to read it. There are many imperfect tense there. It's like your native language you didn't learnt when to use the "past progressive" in English. You just say it because you have heard it a lot of times before. No? 

Greetings from Spain. 

Excuse my English I still learning ^^