When someone asks a negative question, we should give them the information they want. Don’t worry about trying to follow the correct grammatical structure.
For example if someone says “You don’t want sugar?” you can answer with “No, I don’t take sugar.” You should not just say “No”, because then the speaker won't know if you are saying our guess is incorrect or if you don’t want sugar.
When someone asks you, “You weren’t at school yesterday, were you?”, what can you answer if you were NOT at school?
You could answer with “No, I was sick yesterday.” or "No, I was at home yesterday." Or if you were actually at school and the speaker just doesn't know that you could say, “Yes, I was here but I arrived a little late.”
Always shake your head to show something negative and use a positive facial expression for positive responses. For example, if you say “I can’t swim” and you don’t shake your head or give me any facial clues, I might not be sure if you pronounced can’t the same way you pronounce can.
When we say “can”, we reduce the sound to /kÓ˜n/ whereas we pronounce the “a” in “can’t” like /k Ó• nt/ like the “a” in “Canada”. The most important clue is to indicate positive and negative with a shake or nod of the head at the same time. If I say, “I never drink coffee”, I shake my head and make a negative face when I say it.