Douglas, your question prompted me to think about what I actually do, and I realize I do three things:

1. I make sure I haven’t eaten anything that would compromise my palate. Was there garlic in the pasta at lunch? Or onions on the hamburger? Some foods can alter your palate for hours after you eat them. (See Karen’s Risky Relationships blog above on the 8 killer foods to avoid.)
2. I think about what I’m about to taste and think about everything I know about that subject. Then I ask myself what should I expect to find in the wines I’m about to taste. I don’t go into a tasting of rieslings with the same expectations as I do a tasting of Argentine malbecs. Or a tasting of Burgundies with the same expectations as for Oregon, or even California, pinot noirs.
3. I prepare myself to concentrate. I imagine this is a bit like an athlete in the minutes before they start a race, or walk onto a tennis court, or walk out onto a soccer field.

After those three things are done, I dive in!