So, it's my first time putting together a campaign. I do have some ideas due to playing dnd as a player before. I've got a basic setting I want, but I'm not entirely sure how to put it all together. A couple of the players aren't huge fans of pure or traditional fantasy and prefer more sci-fi themes. So I'm attempting to create an interplanetary world. I am desperately trying to avoid cliches. I want the game to be genuinely fun. I also want to create an open world feel, without making it so vague there is no "backbone" or structure. I know everyone has a first campaign story, and I was hoping for some tips and tricks, as well as any extra resources you experienced DM's might know of. :)   

While some people seem to dislike it as "not a real D&D setting", you might look at Spelljammer - which is "D&D in Space". 

So far as I know ( I don't own it ) there isn't a 5e version of the sourcebooks, but there are some online guides of how to convert the existing editions to 5e, if you search around the web.

In general, I advise people trying to create a campaign and/or a campaign world, to start small. Only build the bare minimum around the party, and expand on the world as they go. Highly detail the local town, and the surrounding countryside. Create some detail of the province/barony/dukedom the town exists in. Create a sketch of the Kingdom. Have names and relative geographical locations of other cultures and nations around the Kingdom. Create lots of rumors and legends about locations, and people, and organizations - but only flesh them out fully, or lock down the details as decided if/when the party actually pays attention, or looks, or investigates. Create gods for the party clerics, and perhaps a few rival gods - but no need to sketch out all the gods of your world all at once.

And keep detailed and close notes of the things you do decide to finalize. Once the players learn something, you need to be consistent. 

The trick is keeping up with the players so everywhere they look is vibrant and seems fully realized. What they don't know is where they're not looking, might not even exist in the world, yet.

That keeps your workload low(ish), and allows you to concentrate on depth of detail, rather than breadth of lore.

I keep harping on his videos, but I think highly of Matt Colville's Running the Game  series on YouTube - it's worth checking out for new DMs.

A Spelljammer campaign where your party is moving from world to world, outpost to outpost, seems pretty well suited to that approach, as well. Every new destination they travel to can be small and self contained. 

Then you can start to knit those locations together, with shared plot threads, reoccurring enemies and allies, and the like.

Best of luck!

Thanks so much for the advice. The resources and tips really help! I've taken a lot of ideas from spelljammer now! Thank you! Your workload tip is also helping me keep it super player oriented!

I don't have much more to add other than this: honestly, the best resource is /experience/. The more you play the game, the better you'll get, as with most things. Don't be upset if the first few games don't turn out as you expected! Try to get everyone together to set the expectation of what they want out of the game, and then once you've started, just roll with it, even if the players veer 1,000 miles off course (they will definitely do this)

I would use the world of eberron. It has some sci fi themes.