Some things seem to go into and out of vogue. At the moment onboarding seems to be making a comeback. Onboarding is the inclusion of one or more extra screens to introduce a new user to the app. Smashing magazine has a great discussion and tips on onboarding.
However, my tip is not to go over-board on this. My experience is that most users are impatient and don’t read what’s put in front of them. They try, then question. Hence, also think about how to serve customers when they start to wonder how to do particular things with your app – even if you have already told them in the onboarding. Your support starts with what’s behind a help icon or button.