If you keep an open mind when you hit the road, sea or sky on vacation, you'll have a much better chance of having a successful holiday.

"No matter how much planning you do, do not expect perfection on any vacation because you cannot have that much control," says Stephen A. Shapiro, who has done some serious studying of America's vacation habits. The success or failure of any vacation, shapiro says, depends on a number of variables, including the weather, location, companions and recreation, just to name a few.

"Therefore," he said, "a vacation is not an ideal picture. It is a process of living that one must participate in wholeheartedly, flexibly and with a desire to give oneself the best possible experience."

A psychotherapist, Shapiro is consultant to American Express on the pschology of travel. He is also author, along with Dr. Alan J. Tuckman, a psychiatrist, of "Time Off: A Psychological Guide to Vacations" (Anchor Press-Doubleday, $5.95).

Shapiro says that by having the right attitude, you can even turn a poor vacation moment into a rich one.

"If you are waiting on a long line to get into an attraction, you can make a friend. If it is raining, you can explore shops, museums or go antiquing instead of sitting around sulking about the weather. If your companion is complaining, you can use that to establish a deeper intimacy. A vacation is an act of identity creation. You are making something for youself, and you can make use of anything that comes your way," he said.

Before going on vacation, or even making serious plans for it, you should ask yourself these six questions:

How much time do you have available?

How much money do you wish to spend?

How well do you tolerate the stress of doing many new things in a short time?

Would you enjoy the security and protection that a carefully planned tour can offer?

Do you enjoy the risk of being on your own in a foreign country?

What do you want to do for yourself?

The last question, said Shapiro, is the key one. "It's a difficult question, but it must be asked because it is essential while planning and while sharing a vacation with companions. Your vacation is an investment in yourself."

You can get a free copy of Shapiro's booklet, "Your Vacation Personality," from American Express by writing: Vacation Personality, American Express Co, 125 Broad St., New York, N.Y. 10004. Quantities are limited.