Start here. The first decision players should be able to make is how to approach the mission, and they should enter the fold in a good spot to make a game plan. You might flesh out the area around the main objective to give them a better idea of how and where it exists spatially, or draw a quick map of a building and mark multiple entrances (like a front door, back door, and loading bay). In medias res openings can also work beautifully, as long as you still include a tactical element. “How do we get out of here" is a reliable classic.
ESPIONAGE
Even the simplest “bug hunt" missions cannot exist in a vacuum without information or connected people. Figure out where in your mission info-social-focused players could thrive, and include things for them to interact with. This could mean writing up a few NPCs with clear motivations, assets, and liabilities. It could mean infosec challenges to be overcome, like figuring out passcodes or managing how dangerous information spreads. Before you think of things to shoot at, think of things to talk about.
ACTION
Last (but certainly not least), throw in catalyzing elements for action. Violence is the most obvious choice for action, and many players will jump at the possibility for violent action wherever it exists. The implicit threat of violence, or an imperative to avoid violence, can also be wonderful catalysts. You might deliciously complicate a mission by including a network of neural implants that lock down the entire facility if a soldier is harmed, have the players sneak past a sleeping monster, or rappel down a cliff to avoid being captured.