What will set you apart from your competition?
What do you do better than your competitors? Why are your products superior?
Why should people want you?
What is your USP (Unique Selling Point)? What are your PCR's (Points of Compelling Relevance)?
If you already have a reputation for quality, service, product range, price, or after care then you've got a big advantage over a startup company.
If not then we'll need to discover the hook lines that best describe you.
Then you have to find a way to get your customers to believe you.