Tag questions are tricky even though they look pretty simple. According to http://www.englishclub.com, “A tag question is a special construction in English. It is a statement followed by a mini-question. The whole sentence is a “tag question”, and the mini-question at the end is called a “question tag”.
The main idea is that if you have a positive statement like “You like pizza and beer” the tag question will be in the negative. In this example, the whole sentence with a tag question would be “You like pizza and beer, don’t you?”
If the main sentence is in the negative like “You hate fast food” then the tag question is in the positive. In this case, the sentence with tag question would be “You hate fast food, don’t you?”
For the verb “to be” you use a form of “to be” in the tag question. For other verbs in the present simple or past simple you use “do/does” or “did.”
Finally, remember that tag questions are used for confirmation. You are expecting the person you are talking to to agree with you.