Show us what you have got
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 and inviting their friends is impossible since we do not know who they are.
