Today, due to growth of technology even health may be managed better by both doctors and patients. By now 45% of clinics actively use mobile technologies for communication purposes, data collection, patient treatment and monitoring, etc., as stated in the HIMSS survey. Furthermore patients and even ordinary people who want to stay healthy and monitor their own bodies are now empowered to do so, thanks to mobile tech.
It has to be user-centric, meaning you must create something that solves problems and assists with tasks people might have, and, at the same time you have to know who you are developing the app for, to know these possible challenges people are facing.
Secondly, you have to know and explore full possibilities of devices you are developing for, however you should consider their limitations as well.
Go full on Responsive Design. You never know which exact device people will be using. While creating custom native apps may not always be your best option, usability and user experience are too vital to neglected. With Responsive Design, you app will respond and change accordingly to screen sized, thus more comfort with use and view is granted.
Mobile devices are still not a replacement to desktop experience and, while at home, people still do prefer using their PCs or laptops. By granting synchronization you will improve sales significantly. Just consider the following: 90% of tasks conducted by people are being finished on a different device than the one work began from.
Numerous companies, businesses and clinics now support personal devices doctors and nurses bring from home. This trend grows. So be prepared to extend reach of your application from any dedicated medical device and integrating it into an iPhone or a Mac, etc. It can simply synchronize to allow access to required data, but this functionality has to be considered.
And, of course, security! I believe there is no point in discussing on how vital security is to healthcare software. Just keep all related matters in mind throughout entire development cycle. Test properly, consider all possible design flaws and eliminate possible threats at all cost.
All that noted one last advice: try making things as pretty and simple as possible. Your application is not just functionality! Minimize all possible data input fields (if and where possible), use animations that look appealing, etc. People have to like your app and that is exactly the thing, which will trigger them into choosing you over competitors.