(Excerpt from Rework by Jason Fried)
The way to find the epicenter is to ask yourself this question: “If I took this away, would what I’m selling still exist?” A hot dog stand isn’t a hot dog stand without the hot dogs. You can take away the onions, the relish, the mustard, etc. Some people may not like your toppings-less dogs, but you’d still have a hot dog stand. But you simply cannot have a hot dog stand without any hot dogs.
So figure out your epicenter. Which part of your equation can’t be removed? If you can continue to get by without this thing or that thing, then those things aren’t the epicenter. When you find it, you’ll know. Then focus all your energy on making it the best it can be. Everything else you do depends on that foundation.