I love one shots! It's my turn to DM and always have good fun with them. I've even published a couple on here for holiday specials. Anyway, quick tips...
A one shot is time to have fun with the setting, there aren't real consequences so you can have events happen which would derail a normal session; dragons levelling cities, artefacts of ridiculous power, Gods intervening, wild rewards or else just flipping the players expectations a little. Want to be pirates? Go to space? Run a horror session or a heist? One shot it.
Even with that in mind, you can railroad more than normal as long as the journey is fun, think set pieces... fun new mechanics, puzzles, chases, whatever you like.. watch some of Chris Perkins doing Acquisitions Incorporated for an example of how you can rush through a quick story in a short session with some set pieces
To wrap up a start-to-finish satisfying story in one session you need some structure, I'd 100% recommend a 5 scene one shot, and would follow the 5-room dungeon method (doesn't have to be a literal dungeon). That's (1) Intro/Guardian.. (2) Puzzle or RP.. (3) Twist/Setback.. (4) Climax.. (5) Reward/Revelation/Resolution. Google 5 room dungeon and there are 100s of examples online you can steal from, but this pattern works really well.