"When men speak evil of you, live so no one will believe them!" Remember, your testimony is far more than just words. Your conduct says far more about you than your words do. You may face unjust accusations and outright lies. You may feel frustrated that you can't prove yourself right. Remember - God's knows the truth. And in His good time He will show your integrity. But remember also, Jesus was accused wrongfully as well and He just kept quiet. Again, He knew His Father knew the truth. That was enough for Him. Is that enough for you?
Also, keep a good conscience. You don't want to give the devil a handle in your life that he can hold against you. Be honest from the start and you'll have no regrets.