5. You're willing to run long on consecutive days.
Getting used to running while tired, sore, and mentally exhausted is important training. Being able to push yourself through two possibly grueling days can help you prepare for the rigors of your first ultra marathon.
The back-to-back runs will help strengthen not only your body, but your mind as well. Knowing that you can make yourself run when your legs feel like jelly, you're feeling down in the dumps, or you feel like you can't go any further will help you prepare to push yourself through your race.
More: The Right Recipe for Long-Distance Running
6. You're comfortable eating and drinking during a run.
Knowing your body and what you need to stay energized during your run can make or break your race experience. Use your long runs to figure out what kinds of foods your body can handle on the run. This applies to not only the typical gel or bar, but to other items you may find at an ultra aid station: PB&J sandwiches, oranges, soup, potatoes, cookies, candies, grilled cheese and more.
You may want to experiment with salt/electrolyte tablets as well to help your body with absorbing the fluids you take in. How many you need and how often you need them is something you will need to determine during your training.
More: 10 Natural Race Food Alternatives
7. You don't need to have run a marathon.
There are several ultra marathoners who have never run a marathon (this writer included). This is not a necessary step into the ultra world. The key is more in the miles of training that you have put in.
Having run a marathon may be beneficial. It means that you have (hopefully) put in decent training miles and that you have pushed yourself physically to complete long runs. If you're already a marathoner, you would only need to run an extra 5 miles to complete a 50K race. The building blocks are already there.
More: An Interview with Ultramarathon Man Dean Karnazes
Once you have made a decision to run an ultra, there are other things to consider. Some examples include pacers, drop bags, a crew, and a support vehicle. Some of these things will depend on the race and what the race director allows. Find an ultra that will allow you the time to properly train, and sign up. You'll be addicted in no time.
Sign up for your next race.