It depends on what feels right for you. Feel is hard to describe. Although there are exceptions, I believe most bowlers who use tape put the white tape in the front and the black smoother tape in the back. Some bowlers use only the white, or only the black. There are also different textures to the tapes depending on the manufacturer. Since you described 'slipping' as your problem, you might want to try a piece or two of white tape in the front - especially one with a little texture to it to improve gripping. I use a smoother white tape, but my thumbhole is ovaled and fairly tight - so I never slip.
