Yes, that is a shameless plug.
- Location- the closer to home, the better. Being able to drive offers a huge advantage- you can bring more gear.
- Time of year- it is best to avoid extreme temps that may occur in the middle of winter or summer.
- Race organization- Usually the longer a race has been held, the better the organization. Better organized races usually provide better support.
- Terrain- In my opinion, gentle rolling hills on smooth trails is ideal for a beginner. Flat ground forces you to use the same muscles for the entire distance. Rough terrain or steep elevations make the race more difficult.
- Point-to-point versus loop course- A loop course offers the benefit of having a “central base.” It also allows you to become familiar with the course which is handy later in the race. It also gives you more opportunities to throw in the towel and quit.
- Aid Stations- A good selection of food and beverages is very handy. Some ultras skimp on aid station food, while others have veritable buffets. Also, the distance between aid stations can be significant. Generally, the shorter the better.
- Rules about pacers- A pacer is a non-racing runner that can accompany you for part of the race, typically the end. They help motivate you and keep you on pace (among other duties.) If you have access to a pacer, they can definitely be a benefit for your first ultra.
- Cutoff Times- This is the maximum time allowed to finish the race. Find a race that has the longest cutoff times possible.
There may be a handful of other elements to picking your first ultra, but these should provide an adequate starting point.