My list of grammar and general writing tips. I'll add to this periodically. And remember, rules are made to be broken.
When to use fewer and when to use less
"Fewer" is used for things that can be counted. "Less" is used for a smaller quantity of something that cannot be counted in discrete units.
For example, if you take a sip of water from a glass, you now have fewer drops of water in the glass, or fewer ounces (these measurements can be counted: one drop, two drops, three drops; an ounce, two ounces...).
You also have "less" water in the glass overall, "water in the glass" being a non-discrete quantity.
If I quit my day job, I will earn fewer dollars. Less money.
And if I don't spend a few hours writing today, I will get less of my novel finished... or fewer pages.
Got it? Then a quick quiz:
Question 1: At your favorite grocery store, should the express checkout lane sign read "10 Items or Less" or "10 Items or Fewer"?
Question 2: Can you explain what is wrong with this sign?

Question 3: Which of the questions below regarding the following advertisement is true?

A. Yes, I want less wrinkles.
B. No, I want fewer wrinkles.
C. I don't want wrinkles, period.
D. A and C.
E. B and C.
Answers:
Question 1: "10 Items or Fewer". As you put them on the conveyor, you can count them!
Question 2: "Count" is the key word. If you can count them, use fewer! "Count Fewer Sheep".
Question 3: Either B or E.