Check out some of my resto threads Marty - in particular 0 the Sinbad Resto..

In a nutshell ;

Compressed Air - Clean out the CRAP with compressed air - back and front
Nifti - I love Nifti.. "Nifti in one hand and rag in another"..Spray on the rag, not the playfield
Novus 2 - It is gently abrasive on playfields - test on plastics, and don't do the reverse side of the plastics
Paste Wax - Meguiars' Carnuaba Wax - I swear by this product

Water expands the wood.

I with Nino on this one...

I also love Nifti, but you do have to be careful with it. As Nino has said - never spray Nifty directly on to the playfield, always onto the rag. And don't rub too long in the one place.