Prior to smoking I use a mouthwash;
1 part Listerine (I like the spearmint kind but original works too)
1 part Hydrogen Peroxide (old trick a grand-dad of smoking taught me a few years ago)
1 part water
Cleans the palate right out; usually use in the morning If I plan on smoking in the afternoon. Or before I go out to smoke. You would be surprised at how well it works.
During I just sip on San Pellegrino Mineral water and its a cleanse between puffs.
Honestly though unless I'm smoking a TON of heavy, dark Nicaraguan sticks (multiple ligas, etc.) the day before or of, It really isn't a "must" just take your time and smoke great sticks. Slower smoking keeps the harshness down; "purging" keeps the stick burning clean, and not smoking dollar dog-rockets keeps the smoke enjoyable.