Throw a wild guess if not sure of it?
What kind of app is it going to be (offline/online)?
How you want user to sign-up?
Choose App Language?
How much secure you need it to be?
Does your app contain any of upload feature?
What functionality you want?
Map & Geo Location
News feeds, Social feeds
3D Game Play (if it's a game)
In App Notification
Collecting User's behaviour
Payment Gateway Integration
In App purchase
Please clarify your backend requirements (if any)