If you look at the Wikipedia definition of unique selling Point (or proposition) it defines this as:

1. Each advertisement must make a proposition to the consumer—not just words, product puffery, or show-window advertising. Each advertisement must say to each reader: “Buy this product, for this specific benefit.”

2. The proposition must be one the competition cannot or does not offer. It must be unique—either in the brand or in a claim the rest of that particular advertising area does not make.

3. The proposition must be strong enough to move the masses, i.e., attract new customers as well as potential customers.

It’s difficult sometimes to define what is unique about your business compared to others but if you cannot differentiate yourself from the competition it makes it much more difficult to sell to them and your product or service becomes price sensitive.

Defining your USP requires a bit of creativity and soul searching. A good way to start is to look at how other successful businesses undertake their advertising and the message they sell.

Some businesses define there USP based on service, some on time, some on quality or luxury. A famous example was FedEx’s ‘When it absolutely, positively has to be there overnight – Guaranteed’ in a 1980’s. I think it is obvious to see what the USP was and nobody else was offering this at the time.

Sometimes your USP is just you if you are an expert in your field.