Coldmist Mountain got on the list! You will remain where you deserve to, peasant: at the foot of my mighty Throne of Knytt Awesome! (Now who's ego's massive?)
Actually I think you'll get on the list the same way I did; make levels until you work out what works and what doesn't, listen to the feedback you receive, work out rough guidelines for that fine line between challenging and annoying, and then make a good level.
The first level I made was probably longer than Eurydice, and while it had some great moments, it was also often frustrating, really, really hard, unnavigable and generally not much good. I learnt a lot from that first level, the biggest bit of which was that I wish I'd done my learning in smaller chunks, so more than 1 person would have finished it.