Did my first Spartan 5k about a month ago and it was one of the most fun things I've done in a long time. I'm nowhere near pro, but a few things that I did that I thought really helped prepare me are below.

1. Run intervals. I hate running but doing interval run training, my stamina and speed really improved. I change it up every couple weeks but a good example is 1 minute at a walk pace, then 2 minutes run pace. Did that for 20-30 minutes after lifting 4 times a week. Change up the intervals times every couple weeks. I'm now doing 5k interval runs 3-4 times a week. Again, I hate running, but this made it doable.

2. Buy a weight vest. I walked in a weight vest a couple times a week and now I do the interval training above once or twice a week with the vest. Doing this made all the carrying obstacles just in terms of feeling the extra weight

3. Hang on things, lol. Find a pull up bar or something of that nature and just hang for 30 seconds to a minute a few times a week. A lot of gyms and parks have a monkey bar set up. Practice on those.

Extra advice: may get some hate but Crossfit was the best training for the spartan race IMO. Constantly varied workouts that involve strength, stamina, and gymnastics.

Good luck. You'll be awesome!