Traditional business advice says that if you want to stand out, then you need show how you are different from the competition. Why should someone choose you over the other guy?
Online, however, differentiation isn't as important as inclusion. How do you fit in? How well can you integrate into your customer's life? Why are you a natural choice?
If you think about online services like Google, Amazon, Facebook - these services are extremely popular because they fit in really well with what the user is trying to do - search, buy, connect.
The most important way for you to stand out is to be the one who does something very specific, to create and own a specific category. You see, online, you want to be pigeon-holed. You don't want to try to be "different" or "unique." You want the customer to know exactly where to put you in his or her life.
The trick, however, is to create and manage the pigeon-hole - this way you can control it.
A great example of this is Tim Ferriss, whose book The 4 Hour Workweek introduced a new category in business/self-development: lifestyle design.
Now his name is synonymous with lifestyle design, so that if you want to learn about it, your natural starting point is to read the book.
Thus, if you want to stand out, you need to ask yourself: What category can I create that I can also dominate in? You may not get the category right the first time, but if you keep trying to create them for yourself, then you are way ahead of the game.