How should I decide my niche?

Chose something that doesn't bores you to death and it's not too competitive

The best possible answer that I can give here is that you would need to do pretty thorough research to find and analyze what would work the best for your case. See and dig which are some popular and trending niches at the moment, but also make sure that you perform competitor analysis as well to see how big is competition for popular niches in your market. You should aim to choose one that has potential and can attract the attention of a wide audience, but that on the other hand isn't that saturated and doesn't have many competitors that are targeting it. All this requires some time, but it's a necessary step for achieving good results.

Get inspiration from other people. Use their ideas as a guideline and see if they work for yourself.

It should always be something that you have interest in. Even if you do not have passion to write on own and hire someone for this, it helps if you have some interest in that niche.

You are on an internet marketing forum so this must be interesting for you. Why don't you make a blog in same niche?