I just went through two GMP/AIB audits.
They focus a lot on plant cleanliness. The auditor will look constantly at ceilings and anything overhanging the products critical pathway. They usually carry flashlights and mirrors for looking under machines. So get a flashlight and inspect as they will.
If a contaminant is found in the critical pathway they may stop the audit for an automatic fail. They are usually lenient on documentation NC contrary to GFSI audits.
They also tend to look in unexpected places like the inside of ventilation units. Check for bugs, spider webs and the like. If you have rodent traps make sure they are well aligned against the wall.
They will look at employee sanitation practices, hand washing, hot water availability etc.
If you have any cracked plexiglass on your machines, change it.
Make sure your master cleaning schedule is well filled out and up to date.
Those are a few items, you'll get the hang of it!
Good luck sleeping the knight before the audit ;-)