Having an assault charge dropped is different than being found not guilty of assault. When a charged is dropped, this means the case has been resolved in your favor before the trial begins. This eliminates your need to prove your innocence during the course of a trial. There are a number of things you can do to have assault charges against you dropped.
Call a lawyer. You should never attempt to navigate the justice system without an attorney. You'll need one who specializes in assault charges.
Learn as much as you can about the case against you. Get copies of the police reports, find out what evidence is involved and find out how strong the charges against you will be. In many cases, your lawyer can do this for you.
Discuss possible ways to have the charges dropped with your lawyer. He can often determine the best way to proceed and the formal steps you will have to take to file the correct motion.
File a motion to dismiss. This takes place in the early stages of the trial, when the defendant believes that the evidence is deficient in some way.
File a summary judgment motion. If the facts are not in dispute by either party, you can ask the judge to render a summary judgment. In this case, you believe that the facts are not sufficient to merit a charge, and can ask the judge to render a verdict.
Look into having your record expunged. If the charges against you were dropped, you may want to see whether you're eligible to have your arrest record and other details removed from your record. Services such as those offered on the ClearMyRecord website may be able to help you do that (see Resources below).