There is no "formula" for competitive advantage. You have to do a business analysis and figure out what makes them good at doing what they do.
Do they have better store locations?
Is their product superior?
Do they have better deals with their suppliers?
Do they offer the same products for lower prices than their competitors?
Do they have better time to market with products than their competitors?
Do they manage their inventory levels better than their competitors?
Are they better at marketing their products than their competitors?
Do they have better brand recognition than their compeitors?
Are their customers loyal or not?
Do they have a brand that consumers identify with?
You basically have to study the company and it's competitors and identify strengths and weaknesses. You may (or may not) be able to place a dollar value on those advantages.