There are several different ways to approach this subject.
For example, you could simply make extravagant claims about your product or service.
That is called "huffing" a product etc.
You could study all the features of your product and know the features of the products of competitors.
I propose that you should know how to smile with ease, adopt a sincere look, make clear eye contact without obtrusive staring.
The ancient proverbialism about selling is to convince a customer that they have a problem and carefully outline that problem for them in an objective manner. Then tell them how your product will be a solution to that problem.
There are cunning sales techniques which are devised to circumvent the individual persons exercise of Free Will. Creepy people do this. After the customer says; "No." The sales person begins to use a list of objections and show how their presentation countered all of those objections.
I hope you will not fall into that practice.
A better way is to talk to the people you meet and ask them about their life and activity, and when you have discovered what their need is you can see if your product will satisfy their need.
Good luck WeiWei.