A big issue I run into when I'm working on a game I'm really excited about is figuring out when to inject which idea I have into the campaign.
To put it another way, I tend to have dozens upon dozens of ideas for scenarios, characters, environments, and more and I want the players to be able to experience them all right away. I don't want the campaign to end prematurely for some reason with everyone getting to experience all the cool content I have planned.
The problem is, you can't put several dozen sessions worth of content into a single adventure no matter how much you want to. It just doesn't work and it's a situation I have seen far too many rookie Gamemasters attempt. The desire to throw everything and the kitchen sink into a single sitting will only weigh the game down and muddy the players' understanding of what is (or isn't) going on.
In addition, as I recently discussed with some of my players, sometimes a story works better if other stories are told first. For example, an adventure heavy in action and combat has more weight if you care about the characters involved. You get to care about the characters by first getting to know them.
So, by this thinking, in a new campaign one should have a character study/development focused session precede one in which said characters' lives are in danger. Know that we know who they are, and we want to know even more, no one will want to see them killed off. This raises the emotional stakes and is a lesson I learned from analyzing the better constructed television series.
For my new Red Dwarf/Yellow Sun campaign, I had several session/adventure ready to roll and several more I planned to develop further that expanded the world-building and brought in some of my favorite elements of the TV show's canon. However, after re-watching the entire Red Dwarf show from beginning to (current) end I noticed that the first season was largely explorations of the characters all set aboard the titular vessel. Sure Sci-Fi concepts were thrown in but major components of Red Dwarf's milieu such as GELFs (Genetically Engineered Life Forms) and Swirly Space Anomalies don't really appear until much later.
This, as well as discussions on the subject with the players, convinced me that the second 'episode' of Yellow Sun should be a character driven one. I rearranged the episode order I was originally planning and the results were nothing short of amazing. We were able to pull off the kind of session that had every chance of failing big time. It was both a bit experimental and high concept but because it was really about getting to know the PCs, the Players took it and ran with in. One of the best sessions of anything I've had in a while.
In the end, show some restraint, hold back that epic set piece and army of multi-headed monstrosities and spend so time figuring out who your heroes are. It will feel that much more satisfying next time they fight to live or die.