If you grade yourself as good, you need to be able to back up why you think you are good. An inspector told me a couple of months back that they would be very "surprised" if someone graded themselves as "outstanding."
Have you got your Birth to Three pack? Stick the chart on the wall (they like that.) Do you have photos showing stuff that you do with minded children - they like stuff like that too.
Check through the Standards that you should be working to, and make yourself a checklist that you can work through.
They're very hot on cleanliness - so wash hands for yourself and mindee before and after meals.
How old is your mindee? If still in nappies and you need to change it, make sure you partake in copious hand-washing afterwards, or use gloves. Dispose of nappy appropriately (don't lob it across the room into the bin!)
Make sure your certificate is on display, even it it's stuck by front door with a bit of sellotape.
Have all paperwork ready - includes car insurance (mine checked my MOT too), marriage certificate if you're married ... er ...
... can't think of other things off the top of my head ... will go off and have another think, and I'm sure others will have useful info for you once we get the ball rolling ...