I found a few helpful videos on YouTube (which is a great resource by the way!) These are worth sharing for those either new to fusing or new to the products shown.
I tend to use MR-97, and more recently ZYP (same as MR-97) on casting molds and texture molds, and kiln wash such as Hotline Primo Primer or Bullseye Shelf Primer on slumping molds and kiln shelves. Alternatively on the shelf I use ceramic paper including Bullseye ThinFire and Papyros. The important thing is that you use some type of release between your glass and what it is going to come in contact with during the fusing & slumping process.
While many people suggest a haik brush for applying primer, I use a soft paintbrush and have never had any issues. The problem I have always had with haik brushes is they seem to shed!