1) Stay hydrated. If you are drinking plenty of water, then go have a couple of those glasses as an orange, grapefruit, even tomato or V8 juice (acidic nature of these will help to exfoliate any VG or flavorings films covering your newer taste buds and such)
2) Cinnamon redhots or citrus flavored liquids (you will need a glass or fully metal tank for these plastic tank killers), or cinnamon gum/mints will help spark up taste buds from being asleep
3) Cucumber liquids, yes sounds disgusting, but in fact cucumber somehow is a pallete cleanser, I generally use a cucumber /w spearmint flavor, makes it a bit more pleasant and the spearmint covers most the flavor and is a bit refreshing.
4) If you are generally using rich flavors in a high VG based liquid, custards, bakery, vanilla, yogurts, milky flavors, lay off them for a day and switch to a strong, sharp liquid you can't normally vape (all them blah sample flavors you've collected, now's your chance to vape them and not waste juice), or vape on a flavor completely opposite spectrum of your normal vape
5) Gargle some vinegar and water (tablespoon vinegar to 1 glass of water)
6) Next time you brush your teeth, give your tongue and upper palette a thorough brushing
7) None of these work, get yourself some unflavored liquid and vape on that all day.
Think I covered all the methods