First of all, let's take an example. The following sentence shows four actions the subject(Jack) did last week:
Last week, Jack went to school, studied a lot, was paying extra attention at Math and learned new English grammar lessons.
The fact here is that the sentence above is not correct, because if two or more verbs have the same subject(Jack), then the verbs must be parallel, it means, all verbs used in a sentence must be in the same tense. In the example above, "was paying..." is not in the same tense as the other verbs are, in this way, verbs are not parallel.
So, let's see the correct sentence:
Last week, Jack went to school, studied a lot, paid extra attention at Math and learned new English grammar lessons.
- Another important thing to remember here is if the verb has a helping verb(will, can, is, was, ...) you must use it before the first verb, but it isn't necessary to use it again before the next verb of the sentence. Usually it is not repeated.
Jack will travel and (will) visit new places.
He was walking around and (was) listening to some good music.
She can dance and (can) sing at the same time.
That's it! Best regards!