So under the new system, what actions do you need to take to ensure users come back to your application? Here are the various phases of the application engagement funnel:

1. Collect Email - When a user installs an application you’ll have the option of collecting their email. Whether or not you should prompt them to disclose their email immediately should be determined through A/B Testing. Ultimately this will become one of the most important methods for re-engaging users.
2. Bookmark Users - Whether or not you get the user’s email, you should encourage a user to bookmark your application as soon as the user installs it. As they interact with your app you should continue to promote the bookmark application. Bookmarked applications get a clear benefit over other apps so this step is the most critical.
3. Recently Used App News Items - If the user didn’t bookmark your application and you don’t have their email, you need to take drastic action. By posting news items, there’s a chance they will be visible under the recently used applications area of the Dashboard. As we mentioned above, you aren’t one of the three most recently used applications they will be pushed onto another page.
4. Counters - If the user did bookmark your application you are fortunate. You can now post counter updates to notify the user that there are recent activities within your application that they should take note of. As soon as they click on the counter they will be brought to your application.
5. Fan updates - The last model for engaging users is through targeted updates, if they became a fan of your Facebook Page. You should have a place throughout your application which encourages users to become a fan. This provides yet another way of engaging users.

Useful summary from allfacebook.com for those of us being on the lookout for the coming changes.