Why do you want to run a hackathon and what do you want to get out of it? The point of a hackathon is to generate creative solutions to real problems – usually something that will make a difference to your clients; your business; your people – or all three. Be clear on what you want to gain from it.
Also determine how you will measure success. Our aim was to get more people from outside our development team involved in our hackathon (we did it, with a 121% increase in the number of cross-functional teams from the year before). But you could also base it on the number of ideas generated, or how many projects make it to market.