Human fingers are big. Although the iPhone has a much smaller screen than the iPad, the size and shape of the typical human finger does not change between the two devices. Do not design interaction elements for the iPad smaller than, say 40-by-40 pixels in size.
When in doubt, design larger rather than smaller. The iPad with its larger screen is more likely to be held further away during use than the iPhone, which is often raised fairly close in during use. Build your on-screen objects accordingly. With its 1024x768-pixel screen, the iPad has the room for clean, large interaction elements. Use that space to better compliment the human finger.
Attention spans are short. Like the iPhone, expect your users to approach the iPad in a sporadic netbook-style fashion. Design your applications around short interaction periods and prepare for your application to be cut off as a user stands up to grab his next Orange-Cranberry Frapaccino.
Always save your application state between sessions, as much as you possibly can. A well designed app should relaunch quickly and, upon relaunching, approximate the same task your user was performing the last time the program was run. This can demand diligence on the part of the programmer, but is worth the time investment due to the payoff in user satisfaction.
One more tip after the break!
Thanks Scott Lawrence, |Agent
You've got to launch fast. If users complained about your launch speed issues on the iPhone, expect even worse criticism on the netbook-like iPad. Get your user into your application and started with work as soon as you possibly can. Apps that display credits and launch videos are wasting the user's time. Remember too that larger screen size means larger image asset sizes; which may take more time to load.
Use threads to keep your GUI from blocking on load. A well-threaded app should be able to catch up with the user without blocking the user from getting started. Remember that you're working in a one-application-at-a-time OS. Users will both want to and need to flip from one app to another as e-mail arrives or when checking a reference on the web. By speeding up your application launches, you help ensure that your user can get back to what he was doing as quickly as possible.