How to make a word plural

Just add an s or es. It's that simple, really. We learned this in grade school, right?

Somehow this simple rule has been forgotten by the masses. I see plurals made with an apostrophe and an s everywhere these days.

Here is a good but bad example from Restaurants.com:

The Raven Grill

Open for breakfast and lunch, the Raven Grill offers a casual dining atmosphere with great service and a diverse menu that has become popular for golfer's, locals and business traveler's alike.

Why did they think they needed an apostrophe in golfers and travelers? And if they are following some unknown rule, why not add an apostrophe to locals? We'll never know.

Tip: Never use an apostrophe to make a word plural. Never, ever, ever.*

Even dates and numbers don't need an apostrophe when made plural.

Wrong: I was born in the 1950's
Right: I was born in the 1950s

Neither do capitalized acronyms:

Wrong: Learn your ABC's
Right: Learn your ABCs

Nor do proper nouns, like first names or family names:

Wrong: Tom's, Dick's, and Harry's (unless you are making them possessive rather than plural)
Right: Toms, Dicks, and Harrys

Wrong: I visited with the Smith's
Right: I visited with the Smiths

More examples I often see with apostrophes that don't need them:

ifs and buts

dos and don’ts

threes and fours

thank-yous

maybes

yeses and nos

*OK, you're right, there is at least one exception to the "just add an s or es" rule. It is hardly worth noting, because it tends to make people default to using an apostrophe just to be safe, but I'll include it anyway (I know you're curious):

Wrong: I added xs and ys to my list.
Right: I added x's and y's to my list.

In other words, if you are making single, lower-cased letters of the alphabet plural, you may correctly add apostrophes with your s's.