As different rules and procedures exist for different offenses, you should seek a criminal defense attorney who has worked on your particular type of case to provide you with the best defense. An experienced criminal defense attorney knows what information the government will need to prove your guilt. The defense attorney will also know what information you need to prove your innocence, including whether there are any legal rules justifying your actions.
If you are suspected of driving while under the influence of alcohol or drugs, you may be arrested for DUI (driving under the influence). A DUI conviction has serious consequences (for example, losing your driving privileges); but an experienced DUI attorney can often get the charges dropped or reduced, or may be able to negotiate lesser penalties depending on your circumstances and your past history.