Don't over-mix the batter. Mix just enough with a whisk to barely
moisten the dry ingredients. Ignore lumps.
Ideally, let the batter rest, covered, in the refrigerator for 3 to 6
hours.
Variations in the moisture content of your flour will require
adjusting the batter thickness. If the batter is too thin, add more
flour. If the batter is too thick, add more water.
If making waffles or if you just want to avoid having the pancakes
stick to a pan, add an extra 2 tbsp oil or butter to the recipe.
Frozen blueberries have more moisture than regular blueberries. If
adding them, thaw them under running water and then dry them a bit. If
you mix them into the batter they will color it, so instead sprinkle
them onto each pancake after pouring out the batter.
References
The Joy of Cooking, 75th Anniversary Edition, p 643