Great question -- I'm a Product Manager on the Eventbrite API, so I'd love to help you out.
On the /event_search API method, there is an argument that you can set for how you sort the results -- you can set "sort_by" to a couple different values (Date, ID, name, and city). I would recommend sorting by ID, because it's the most consistent.
Once you do an initial pull from our directory, you can pull a subset of the total events by filtering on the 'date_created' or 'date_modified' arguments... so that you're only receiving events that have recently been added or updated.
Here is the documentation for the current /event_search API: http://developer.eventbrite.com/doc/events/event_search/
Hope that helps!