If you want to get into the business of designing apps, there are a few key rules that you should try to keep in mind.
You should apply the rules of interaction design. These should not be allowed to slide just because you are developing an app for a small screen. Make sure that you are designing for the right user and that the app itself is user-friendly. Learnability is another important factor – you do not want the user to have to spend a long time trying to figure out how to use the app. There are other rules that you should also familiarise yourself with.
The End User
It is important to keep the end user in mind when developing an app because these are the people that you are designing it for. Consider features such as the user scenarios and experience maps that will help you to work out the reaction of the user while the app is in use.
Familiar Mobile Patterns
The design of a good mobile app will need to take into consideration the nuances of the specific device. This might include things like the thumb placement. It is a good idea to look at the most common mobile patterns and this will help you to design an app that the user will feel at home with immediately.
This might seem like a strange rule to consider but you have to remember that fingers are fairly thick, so the design needs to be easy to use with the fingers. Space needs to be added that gives the user total control with their fingers so you cannot make the buttons too small or place them too closely together. Users will not stick with an app if they find it difficult to control it.