How an attorney dismisses a ticket varies widely depending on the traffic infraction alleged and the state laws that were allegedly broken. For example, if you received a speeding ticked but your state has “presumed” speeding laws that loosely define the speed limit then your traffic ticket attorney may argue that you exceeded the speed limit in order to maintain safe speed with the rest of traffic or to overtake another driver.
Another example would be if your traffic infraction included allegations of driving under the influence. In that case, the attorney would likely scrutinize the testing process, arresting officer's testimony, or other parts of the process that may have incorrectly led to your being charged.