Where and how should you listen for entry delete in plugin? When an entry is created with my plugin's field type, data is saved to a separate table with entries id for reference. I need to delete that data if the entry that is associated with the data is deleted.  How and where should I listen for entry delete event to execute a method to delete this separate data?
You can add something like this to your plugin's init() method:

craft()-&gt;on('entries.onDeleteEntry', function(Event $event) {
    // Do your custom logic here.
    // Note that you can access the entry that was just deleted via $event-&gt;params['entry']
});


Or, better yet, from your custom table, make sure the foreign key that you've created on your entryId column back to the entries table has a CASCADE DELETE setup on it so that when Craft deletes the entry, it will cascade down and delete it from your table as well.