1: Find Your Trip/Challenge:
Pick point A and Point B that you are going to run/swim/ride/paddle/handstand between. It doesn't need to be a record or the most scenic route ever, it needs to be something you want to do (sometimes making the start and finish line a common location can make the trip easier for your audience to understand and follow).
Work out your trip logistics early (gear, support, weather etc.) so you can depend on your planning once you do go public.