Hello!

You can either take weekend coaching for entrance exam along with class 12th if you really want to persue a professional course, otherwise it might be difficult for you to manage both boards and coaching together.

Or You can Refer to Entrance Preparation books and be aware of current affairs through out the year and after your boards, take up a crash course, usually of a 3 month. The Crash courses are really good to evaluate yourself using the mocks.

If you are really good at self study, then focussing on 12th would be better while alongside preparation of entrances.

All the best!