When approaching effective mobile UX design, there are a few golden rules that will always allow developers to reap the rewards.
If developers adopt these principles and adopt them early, much good can be accomplished. Such principles will be limited in efficacy if they are used as after-thoughts, tacked-on to the development process. Study these principles, understand them, and use them as both the datum and bedrock of your designs. These rules are fundamental principles and must be treated as such; they are not the final flourish, but the backbone of your app designs.
Targeted interaction design
Mobile apps have less screen space at their disposal than desktop applications, but good interaction design is still possible. The very personal relationship between the user and mobile device is a fertile soil where the seeds of interactive design can bear abundant fruit. Identify the user you are hoping to appeal to with your app and work out good ways to make your app interactive with that target demographic. What will that user-type find engaging, useful, amusing? What ingenious ways can this be achieved with the screen space and interface options available?
Everyone knows how important first impressions are, and apps are no different. Good app design makes for a fluid onboarding experience for users; there must be 'flow' from the press of the app icon onwards. Some apps may have excellent functionality, yet poor onboarding may result in a staccato user experience. Choppy, stop-start app flow will alienate users and spoil the app's excellence in other areas.
Again, knowing your target demographic will be helpful in designing onboarding. Know who you want to appeal to, and conduct research into how to make your app a better fit for them. Remember, you must achieve flow, and you will achieve little if you go against your user's grain.