In order for a driver to be pulled over, an officer must have an "articulable and reasonable" suspicion that traffic laws have been violated. For example, if you are traveling at 20mph over the speed limit, then there is a very clear reason for an officer to suspect that you have violated traffic laws. Speeding may be one indication of an individual driving under the influence, but there are also many others.
What comes to mind most commonly are the "usual suspects" of DUI behavior. These are the classic swerving, erractic driving and running stop lights and/or stop signs. So, when you are pulled over, the officer needs a clear reason to do so. If an officer sees you and, for example, finds your hair to be disheveled and then trumps up a reason to pull you over, this is not a valid reason to stop you and it can be challenged.
You need an experienced attorney who can examine the evidence of the case to make sure the prosecution is following all the legal steps to bring charges against you. You also need an experienced attorney who can challenge those charges and fight to maintain your innocence.