I am in 12th standard. Which course should I opt after doing 12th in commerce with maths?

All market related, sales management, accountancy and banking to name a few. You have varied prospects.

If you prefer to do commerce, you can try B.Com or even CA basic level. You can apply your skills related to numbers. If you are particular about Maths, you may choose B.Sc Maths or statistics. All these courses are good and lead you to great professions.

Try to understand your nature. I mean make a list of your interest of courses. Do a research about them. See your compatibility with the work type of that industry that will be beneficial to you.