If it's a single episode I would love to do one that ditches the main cast to tell a short story about life in the Star Trek universe outside of the normal stories. There was an absolutely fantastic episode like this in Star Trek: The Next Generation called Lower Decks. It focused on a group of junior officers who were being evaluated for promotion. The episode was written as if these characters were regular members of the crew with their own established personalities, quirks and interpersonal relationships, even though we as the audience had no prior knowledge of them. It was a great glimpse into life on the Enterprise outside of the main bridge. This is the kind of episode I would want to make.
Having served in the military myself I would draw on some of those experiences and create an episode focused on a Star Fleet security team, which is the Star Trek analog to soldiers. The story would begin with the main crew returning from an away mission saying they had discovered some things that need further scientific/archeological study. However the Enterprise is scheduled to be involved in other duties and the nearest research vessel is weeks away. So the captain orders a research team to stay behind while the Enterprise completes it's primary mission and can then return for pick up. A security detail is left behind as well because the planet is unknown and unexplored.
Along the way there will be conflict between the science team's sense of curiosity and the security team's sense of caution. So a scientist might say something like "Our mission is to explore this area for valuable knowledge" and a security officer retorts "Your mission is to explore this area for valuable knowledge. My mission is to make sure you live long enough to share what you have discovered."
But it won't all be head butting and arguments. There will be security personnel very interested in learning about the discoveries. Likewise there will be scientists who really listen to the security briefings and show what they learned by getting themselves out of trouble without help.
Dangers initially come in the form of the environment (radiation storms, rock slides, ect) and carnivorous plants/critters. Eventually they discover there are also intelligent beings that see the Star Fleet team as intruders. This raises the stakes and the team doesn't have the Enterprise leadership to help negotiate.
On a side note, I'm going to say that it's a shame that Star Trek Phase II was cancelled before it had the chance to make it to the airwaves. But some of the ideas for the series were incorporated into the Motion Picture.