It’s not an iPhone
The Apple Watch is a different device, used in different contexts, with completely new use cases, and different specifications and limitations than we’re used to. Designing your Watch app is not about translating your app to a smaller screen. The digital crown and screen make scrolling pretty pleasant, but it just doesn’t feel right to have endless streams of content on the Watch. Focus and filter.
Limited screen estate makes it an interesting challenge to give your app it’s own identity. Most apps that I’ve seen still lack some personality, probably mostly driven by constraints of the SDK and performance of the device. There’s plenty of room for creativity on a small screen, although it probably takes a deeper understanding of Watchkit, technical creativity, and performance testing.
Speed is a challenge
The Watch specs are not comparable to your new iPhone 6. No big deal, but it requires a different development and design mindset. Any heavy lifting can take place on the iPhone, be super selective in the content you’ll transfer, preload data whenever you can (on the iPhone), and be smart about caching. Implementing a loading indicator is probably a bad shortcut and not the best way to solve your performance issues.
Use the force
Use your app on the iPhone to do all the heavy lifting. You can go pretty wild with pre-processing data, preloading in the background, and image editing.
You can embed images in your Watch app (up to 10mb), load images via your Watch extension on the phone and cache them on the Watch (up to 5mb), or just load content on the fly. Transferring data via Bluetooth takes time. Include assets in the Watch app when possible (fastest and quite some storage), cache images whenever possible (first load will be slower) and optimize images as much as you can.
We generate and resize some images on the iPhone before sending and caching them on the Watch. Prepare Watch content on the iPhone when a user opens your app to save response time, whenever possible.
Hand-off could be big
You can use Hand-off to seamlessly switch from the Apple Watch to your iPhone and continue where you left 0ff. My guess is that people barely use hand-off in iOS right now, but it could be a great way to take tasks from the Watch to your iPhone.