Once you are arrested for DUI you are legally required to submit to a chemical test. There are additional consequences to refusing a chemical test. The DMV will likely suspend your license for one
year and if you are ultimately convicted in court the judge can consider refusing as an aggravating factor and increase punishment.
Whether or not refusing ultimately will help really depends on the specific facts of each case. The government may already have enough evidence to convict before the decision to submit or refuse a chemical test was even made. Officers are trained to look for objective signs of intoxication and their police reports almost always say that the suspect displayed them. Objective signs of intoxication include an odor of an alcoholic beverage on the breath, red/watery eyes, an unsteady gait, and level of cooperation. The officer's report will almost unsoundly state that the Field Sobriety Tests were not completed properly as well.
As stated earlier, once arrested for DUI the law requires the person to submit to a chemical test. However, prior to arrest there is no legal requirement to submit to any test. You cannot be forced to incriminate yourself. You do not have to tell the officer how much you have had to drink and you do not have to perform any Field Sobriety Tests. You are only required to submit to a chemical test if arrested and by submitting to these test prior to arrest all you are doing is incriminating yourself. My advice to people who are pulled over by law enforcement and they suspect you of DUI is to be courteous, but don't answer any questions beyond providing your basic identification information. Certainly don't tell the officer how much you have had to drink, and do not take the Field Sobriety Tests.