What should you do if people accuse you for doing something you didn't do?

Ok this is a Hard one, I got through this a lot. What i do is i just take my time and let them figure out that you didn't do it, You want to give good evidence that you didn't do it. Now if you got accused of something big, you should talk to a friend maybe he was there and he could tell everyone that you didn't do it. They do these things in court (They are Similar).