While it may seem obvious from looks alone, it can be very easy to misunderstand the way that an Apple Watch differs from an iOS device like an iPhone. Many make the mistake of only focusing on how to shrink the user interface of their app into a smaller form factor, instead of really understanding how the Apple Watch is actually used.
Before we can move on to the more technical aspects of creating an Apple Watch companion app, it's important to look at these differences in use and expectations.
The most obvious difference between an Apple Watch and an iPhone, and I've already touched on this a few times, is the size. There is no way around it. The amount of screen real estate severely limits how much information can be presented, and how many inputs can be accepted.
A lot of developers also seem to underestimate how important it is that the watch is worn; it's not a device that comes out of a pocket when needed. There's a level of intimacy not present...