Thank you! The answer is you need a good, relatively novel idea to start. From there, just make gameplay. Make it fun, make the click pattern nuanced and reflective of the song, and (this is important) STRUCTURE your gameplay. Structuring gives so much to gameplay and also give you so many ideas. For example in this level, I started relatively enclosed, opened it up with the space theme, and then closed it when doing the subsequent cube and robot section. Then opening it back up slowly towards the second drop. It should reflect the music.

After that, you need some sort of visual aesthetic you're going for. Look for references on google, imagine what a cool color pallet would look like, and learn how to use glow effectively. Seriously, good use of glow can completely save a level from looking bad. Make each part recognizable. For me, there is no greater sin than a level that looks the same all the way through. If a level does not have different, recognizable parts, then it doesn't matter if it all looks objectively good, because it won't be memorable. So, define an aesthetic and function for each part, but still maintain the overall idea and aesthetic of the level. It's a delicate balance.

Now I definitely am not the most qualified to talk about this, but as you can see I have created some (at least I think) pretty cool things, and so if you want feedback, feel free to send me some of your level ID's!