Once you have determined your venue location, make sure you walk and inspect the site or venue...more than once!
It helps to walk and visualize where things will go, something you can't do by just looking at a floor plan or overhead map. Small issues crop up that affect where things will go and must be dealt with by walking the event site.
Creating a site map is a good idea as well. It doesn't have to be complex or complicated, just something you can share with your team, the public and suppliers to let them know your general set up and info about your event. There are many ways to produce one from a hand drawn version to a professionally scaled AutoCAD map. Depending on your budget, use what works for you. As your event grows over time, consider a professional mapping service if budget permits. Having a scaled site or floor plan professionally produced can be a big plus.
Some important things to look for on your site/venue visit are things like water access, power outlets and service, pedestrian/guest access, toilets, sight lines, and parking availability.
See the attached files and pro tips for more in depth checklists and links for your site/venue visit.