In the menu bar click "Run" -> "Debug Configurations...".
In the popup dialog right click on "Eclipse Application" in the left hand side tree and select "New". A new config is created.
On the right hand side choose a name and select the tab "Plugins". Ensure that "Launch with" is set to "all workspace and enabled target plug-ins"
You may also want to specify additional VM arguments (like "-Xms256m -Xmx512m -XX:MaxPermSize=256m" for instance). This can be done in the "Arguments" tab.
Then press "Apply" and "Debug". A new Eclipse instance is launched with the plugins in your original workspace loaded. This allows you to debug through the SDK code while performing UI actions in the second eclipse instance.
Hope this helps. If you have further questions, don't hesitate to ask!