can we omit the subject while talking?

Question

ı have read a book and heard of it a lot.someone is talking and says"could not sleep last night" or "just preparing" sentences like that can we always do this or just only while speaking

Answer 1

It is almost always important to include the subject. We can omit the subject when speaking if we are responding to a question/ statement and our answer refers to the original subject.

For example:

Person 1: Did you like the ice cream?

Person 2: Not really

In writing, unless you are writing a dialogue, you always need to include the subject. "Just preparing." cannot be a sentence on its own.