The big question the Guard boards grill people on is how they plan to balance work/life and the Guard. This is not typically as big a deal, but pilots are expected to come in pretty frequently, preferably above just meeting their minimums. This can be a weekly obligation. I was NS for my first board in another state, and upon getting in touch with board members they told me they were apprehensive about my distance from the unit and if I were to board again would like to see me better articulate a plan to regularly participate. Make sure you have a solid plan that you can articulate to them as to how you are going to balance work/life and the pretty significant guard obligation. It's also probably a good idea to communicate that you understand this can be a sometimes multiple days per week obligation, and you are already planning around that. Be able to demonstrate how that will mesh with your civilian job.
Other than that, expect the typical questions: Tell us about yourself, discuss a challenge you had, how do you deal with stress, discuss a mistake you made, etc. Also, there will be a secondary board if you are selected known as the "fedrec" board. This is more or less a rubber stamp from what I gather, assuming you made it past the much more selective aviation board.
There are still the same basic requirements for Guard, but the accession process, packet requirements, etc may vary a bit.