How to choose niches?

Blogging is a very good career option which gives us better work opportunities in the form of part time or full time. Nowadays many people want to start it and many of them started their career in blogging.
During the initial period they decided or chose blogging for the purpose of money only, they would have to change their mind first because blogging demands patience with regularity and with a proper niche which helps to enhance your blogging career.