Write down everything that could possibly go wrong, whether it is big or small.

Include everything that you can think of as relevant. Brainstorming is ideal here, as it is likely to get all the ideas out. Then you might want to group the ideas into themes. Although this is not essential, it can be helpful where you have identified a lot of risks, as you can then produce a summary risk register, with one over-arching risk for each theme. You can also see where your risks overlap, and ensure that each one is genuinely different, and it is easier to think about who might take responsibility for each.