You have a right to remain silent. Use it
Even if you haven't been placed under arrest yet, you do not need to answer questions about where you've been and what you've been drinking. BE POLITE, GIVE THE OFFICER YOUR DRIVER'S LICENSE AND PROOF OF INSURANCE, but don't offer up any more information. EVERYONE says they've just had one or two beers. DO NOT SAY THIS. Just politely tell the officer that you would like to speak to an attorney before answering any questions, and remain silent after that.
You do not have to submit to field sobriety test
Again, be polite, but refuse to submit. Any slight stumble or shaking can be used as evidence against you, even if you're just trembling from nerves. Don't be rude, but let the officer know that you will not submit to testing without speaking with an attorney first.
Portable Breath Test
these are handheld devices used at the scene of the stop to measure your blood alcohol content. These are not the breathalyzer machines that Missouri law requires you to submit to, and their results are not official, but they can be used in building the case for probable cause against you. Do not submit to this test. One way to know if it is the official breathalyzer test or not is that the officer will read you the implied consent warning before asking you to submit to the official breathalyzer test. Whether or not you should submit to that test is discussed below.
To blow or not to blow
there is no one right answer to this question. It depends largely on the circumstances of that evening, your personal history, and a myriad of other factors. When the officers read you the implied consent law, they are required to give you 20 minutes to contact an attorney before answering. Utilize this right and contact an experienced DWI attorney immediately.