Salam ,
Rightly said by mainna.
Jokes apart,

You should be very sure about the topic yopu select. What you know about that topic?

If it is a creative wtriting, you can start as per your own choice...from anywhere and link it to the theme and develope a plot with introduction and sum up with a punch.

Then many things you will leran once you start writing . Start is the key word.

wassalam