How do you guys design levels and start projects?

[Magician]

How I get ideas:
Whenever I see something I don't like in an episode, I think of how I'd have done it my way.

Whenever I mess around in SMBX and discover something unique or interesting, I think of how I'd turn it into gameplay.

Whenever I see someone say something is "impossible" in SMBX, I brainstorm over how I'd make it possible (some of my absolute favourite ideas have spawned from this kind of thinking).

Beyond that, I sort of get inspired as I think about and do things.

I think at the core I'm inspired by gameplay, but I think the stories I come up with that surround the gameplay are pretty solid. My first Castlevania-inspired episode got too complicated pretty quickly, so I came up with a simpler episode design idea so that I could focus less on how to piece everything together and more on just platforming and enemy placement. Then, I ended up connecting the stories in each episode. Then THOSE stories inspired two other episodes, and...

As a result I have a pretty clear core concept behind seven different episodes. I should mention that two of those episodes are extremely short (like maybe 10-20 minutes a piece) and one of them is intended to be an anthology.
I've come up with other episodes as well but discarded them. One of them was a Mario Party-style episode intended for a 4-way screencapture Skype call and a scorekeeper/game master, but I just didn't think it would be very interesting since it wouldn't be 4-player interactive and would mostly involve racing minigames with no sure-fire way to sync everyone, and they'd all have to co-operate with the game master.