DUI cases usually have four types of evidence. 

1. The driving pattern that lead to being pulled over.
2. The physical appearance of the driver.
3. The results of a field sobriety test
   
4. The results of a chemical test
   

There are two main ways a prosecutor usually attempts to get a DUI conviction.  The easiest way is to show the driver's blood alcohol level was above the legal limits.  The second way is to show the driver's physical or mental condition was impaired by alcohol or any other intoxicating substance.

Discrediting the blood alcohol level test results is a difficult, but not impossible way to beat a DUI charge.  A defense attorney can attack the blood sample.  For example, If too much time elapsed between when the sample was drawn and when it was tested, a good attorney can argue the blood had a chance to ferment and thus yield a higher alcohol content.  In some cases, the attorney can attack the lab itself.

Discrediting the field sobriety test is easier, especially if the driver pulled over promptly after using his turn signal and parked safely.  It could be argued that the driver made a traffic mistake, but was not impaired and only failed the field sobriety test by a small margin.  Some people have poor balance to begin with and do not test well under pressure.  A defense attorney could argue that a better test of impairment allows time for students to study beforehand instead of taking it on the spot; that they get to do it in a quiet room instead of outside with distractions like traffic rushing by; and that getting 10% of the answers wrong should’t necessarily result in a failing grade.

These are just hypothetical way one might beat a DUI charge.  You should consult with a qualified DUI lawyer with many DUI wins to increase your odds.

The best way to beat a DUI is to never get one in the first place.  If you are convicted, consider attending Alcoholics Anonymous meetings and get them to sign an attendance card.  Judges are often more lenient if the defendant shows remorse and has taken proactive steps to change behavior.   With any luck, you will learn enough there to avoid a second DUI conviction.