What is a counseling session with the FSDO/FAA?
A "Counseling Session" is the lightest slap on the wrist the FAA can give you (aside from doing nothing).  

Basically it means "you screwed up, you know you screwed up, and we (the FAA) know you know you screwed up" -- they just want to sit you down with someone from the FSDO (probably a FAA Safety Team representative) and have a conversation to make sure everyone is clear on what happened, how the violation happened and that you know how you can avoid this sort of thing happening in the future.

My understanding is that counseling sessions are "informal" (they're not an official "administrative action", so I'm pretty sure they don't go on your airman record) - the FSDO will note that they talked to you and bury that tidbit in their internal file, to be generally forgotten unless you decide to make a habit of busting airspace.

(The closest "official documentation" I can find on counseling sessions is in the FAA Safety Team's Representative Manual -- Page 12 if you're interested.)



Some things to bear in mind:


You're the kind of pilot the FAA isn't out to beat up on.
Yes, you screwed up - but you know that and you clearly want to make sure you don't do it again, which is really all they want too. 
Make sure you're clear in your mind what happened &amp; how to avoid similar incidents in the future.
Did you misread the chart? The altimeter? Get distracted looking up the frequency? Something else?
Don't admit to any other violations during the counseling session.
(Presumably you didn't commit any, you got a proper flight briefing, etc.)
Hang on to your ASRS strip.
You won't need it for a counseling session, though mentioning you've filed an ASRS report won't hurt anything. If the FAA opts for a more formal action that strip is going to be important.
If you have AOPA pilot protection services now would be a good time to chat with them too, just to cover all your bases.