He's only 9, but this pint-sized pickup artist already knows plenty about pleasing the ladies.

So much, in fact, that Alec Greven's dating primer, "How to Talk to Girls" - which began as a handwritten, $3 pamphlet sold at his school book fair - hit the shelves nationwide last week.

The fourth-grader from Castle Rock, Colo., advises Lothario wannabes to stop showing off, go easy on the compliments to avoid looking desperate - and be wary of "pretty girls."

"It is easy to spot pretty girls because they have big earrings, fancy dresses and all the jewelry," he writes in Chapter Three.

"Pretty girls are like cars that need a lot of oil."

He advises, "The best choice for most boys is a regular girl. Remember, some pretty girls are coldhearted when it comes to boys. Don't let them get to you."

Over a few Shirley Temples yesterday at Langan's on West 47 Street, Alec said that he culled his wisdom by peeking at his peers at play.

"I saw a lot of boys that had trouble talking to girls," Alec said.

As for his how-to, he concedes, "I never expected people to buy it like a regular book in a bookstore."

But with classic plain-spoken advice - like "comb your hair and don't wear sweats" - it's no surprise his 46-page book was a hit with boys and girls of all ages.

He believes the best way to approach a girl is to keep it to a simple "hi."

"If I say hi and you say hi back, we're probably off to a good start," he said.

As for his own love life, he said he is not dating anyone at the moment. "I'm a little too young," he confessed.

In his book, published by HarperCollins, he suggests holding off on falling in love until at least middle school.

Dating - which he defines as going out to dinner without your parents - is for "kind of old" people, who are 15 or 16.

Officials at the Soaring Hawk Elementary School said he wrote the book - which was the runaway bestseller at its book fair - for kids, but believe anyone can find inspiration in it.

Alec's mother, Erin Greven, credits her son's beyond-his-years insight to his avid reading.

"He reads nonstop. At dinner, I say, 'Put your book down,' " she said.

Alec - who just finished a children's book on the Watergate scandal - said he wants to be a full-time writer when he grows up, with a weekend job in archaeology or paleontology.