Typically a driver is stopped because of a traffic or equipment violation. Depending on the location and time of day, the officer may or may not start off with the assumption the driver has been drinking.
The first thing you want to do is get your driver's license and insurance card out before the officer approaches your window. If you show the slightest difficulty in getting them out after he asks for them, he will note that you fumbled for your license when he writes his report.
You always want to be polite. Always remember that it is the officer who is going to decide whether or not to make this a DWI stop. If you are rude and combative, believe me, that will make it into the officer's report as a sign of intoxication.
Generally if the officer asks you to get out of your car you are going to be arrested whether you perform any of his coordination exercises or not. Do not lean against your car after getting out. If you do, the officer will indicate this as another sign of intoxication.
Listen carefully to the officer's questions and, if you choose to answer them, only answer what is asked. If you've been drinking, your breath will have the odor of an alcoholic beverage; remember this if the officer asks if you've been drinking.
Before you agree to perform the officer's coordination exercises you need to realize that every question the officer asks you and every task he asks you to perform are designed to gather evidence that will be used against you.
If you were stopped for speeding or for an equipment violation you need to be aware that neither of these is an indicator of impairment. Even if the officer notes you had the odor of an alcoholic beverage on your breath, slurred speech and bloodshot eyes, without any signs of impairment, the officer cannot establish probable cause to arrest you (though you will be arrested).
If you are familiar with the coordination exercises the officer will ask you to perform and you know what "clues" he's looking for then you may decide to perform them -- although I would counsel against it. Just remember, even though there are 93 components to the walk-and-turn test, for instance, the officer (and prosecutor) will claim you are intoxicated if you exhibit 2 or more "clues."
If you were not involved in an accident and you don't have a child in your car and the local police are not running a "No Refusal" weekend, do not blow into the breath test machine. I repeat - do not blow into the breath test machine. If you blow over .08, you've got problems, if you blow under .08 the officer will find some reason to explain the score -- maybe you "elmininated" the alcohol from your system or maybe you were also doing either prescription or illegal drugs that "synergized" with the alcohol and caused impairment.
If you are subject to a mandatory blood draw if you refuse the breath test you sit on the horns of a dilemma. If you think you have an alcohol concentration of less than .08 then you probably should blow into the machine. Otherwise you will be looking at a blood test. While a jury is trained to think of blood tests as infallible, there are a number of evidentiary issues that can keep a blood test out of evidence, or at least cast serious doubt on its accuracy.