I've been learning all the rules and cases of usage 了 (le) in Chinese (perfect aspect, modal participle and different structures) but I don't feel confident when using it when talking about past actions. Please, help me to understand how to use that correctly!
I know that the rule says that if we did something regularly in the past, then we don't need to put 了 in a sentence.
But when it comes to me that I'm going to tell a story (for example, about a particle day but in the past) I'm not sure how to use 了. For example:
昨天我去大学（了）。 I go to university almost every day, it's a habitual action but do I need to use 了 here because I'm speaking about the particular day and the moment of my life?
The second question is how many 了 should I use when talking about the past in every sentence? I mean, is it necessary to put it in all the sentences?
Please, help me! I feel so mixed up with that grammar. Thank you in advance..