An alternative approach is instantly showing the content of the app (if the nature of the app allows you to do so) and only asking for a social sign-up when needed.

This way no or little introduction is needed. Just as is the case with many e-commerce solutions (think of web shops), signing up is requested only when it matters. In the case of a web shop, this is required for check out. For a mobile app, it may be applicable, for example, when the user no longer just consumes but also wants to contribute to a stream. You can think of a news app that allows users to comment about the messages that appear:

This lowers the barrier even more; however, the downside can be that a large number of users will never sign-up and for that reason will be less valuable to you. For example, anonymous users are not likely to share a lot on social media from your app...