Have the welcome screen show up with all the new features every time the user updates the app and create a list of all demonstrated features (using an SQL database - on upgrade feature) and hence show all previous feature demonstrations that a user might have missed in previous version (eg: when the user installs the app for the first time at version 1.5, show all major features of the app instead of just the latest features).
Also make sure that the user only sees the major features after installing the app for the first time and not all the features and updates of all time!
Have the welcome screen show up with all the new features every time the user updates the app and create a list of all demonstrated features (using an SQL database - on upgrade feature) and hence show all previous feature demonstrations that a user might have missed in previous version (eg: when the user installs the app for the first time at version 1.5, show all major features of the app instead of just the latest features). Also make sure that the user only sees the major features after installing the app for the first time and not all the features and updates of all time!