What should I do about my student visa before leaving Thailand for Taiwan and returning on a 30-day exemption?

In my case is that: i also had student visa and i asked the school cancel for me because i heard if i didnt cancel I wouldnt do student visa again. And i asked school if i needed any docs to go out and they said no. I did visa run at border n came back with tourist visa again and there was no problem. But I really don’t know if i can do student visa again.

It depends on if you are on the original non-ED visa, or if you are on an extension of stay for studying. If you look in your passport and see something that says "extension of stay" then you are on an extension and you have to cancel it. If you are on the original visa then you cannot cancel a visa and you can just leave the country.

In order to cancel it you need a letter from your school that says the date you will stop studying, and then you need to take that letter to the immigration office that issued your extension. You can go about 1 week ahead of time, and they will cancel your extension and stamp you in until the date on the letter.

If you have an extension for studying and do not cancel it you will not be able to get a long-term extension in the future, and if you apply you are likely to get fined 20,000 baht for failing to cancel your extension in accordance with the documents you signed to get it.