I read that to start in real estate, we first need to find a niche like single family, multi family etc., and a strategy like flipping houses, buy and rent etc.

How can I choose what kind of niche and strategy is better for me?

I would start off with how much money I have.  That may eliminate some choices 

Next I would determine how much of a loan Incan qualify for 

Next I would access my skills of rehabbing a house or overseeing the rehabbing of a house 
what my long range goals are 5 year and 20 year 

What my 1 year and 1 month goals are 

For me this narrows things down pretty good and I can choose from there 

I agree with Michael above.  And would add.  Take a sampling of each of the niches.  Then, practice the numbers for each of the strategies.  What resources and knowledge do you need?  You will see where your passion leads you towards and where you can start, then grow and diversify from there.  Happy Investing!