Most people start the concept of positioning this way:
(1) How do I think the competitors are positioned and where can I position myself so that I can stand out and get more market share.
(2) Then position based on features or products. Example: the fastest, the cheapest the highest quality, local etc.
The problem with this way is that it's competitor focused and focused on your goals. The customer doesn't care if you want more market share and if you want to push your competitors to the side to make a buck - they are looking for something more deeper then that.
This model also fails to understand what's going on in a human's mind when they are positioning products in their mind. Sure some people will say in their mind "what's the cheapest" then go to that product category but most of the time they position their products based on unsaid emotions and desires.
The position in their mind by thinking / feeling:"this feels like a company I grew up around:
"This brand feels safe and trusted"
"People I aspire to be like use this brand"
"This brand helps me fit in or standout"
"This brand looks like another brand I like"
Instead of positioning on logical features, it accounts that we are dealing with the human mind and heart. If done correctly, instead of building these dimensions on competitors in the market, we can make these points based on the markers in the customers mind.