Your Unique Selling Proposition means “why should people choose you over all the other options available to them, including the option of doing nothing at all?”
So, why should your potential customers choose you?
What do you do that is so great? Are you the cheapest, quickest, fastest, quantifiably better, first ever … etc etc. Clarifying in your own mind exactly why people should choose you will pay great rewards later (and remember to ignore the “because we’re the best” type sentiments because they are worthless to anyone apart from you!)