I actually had no thinking building my level in the past, i just opened them and saw if i could come up with something. But i recently started approaching my levels in a very different way.

1 - i dig a lot and i find the song i like

2 - i make a whole text organizing theme and finding ideas from ideas

3 - just before i decorate the part, i draw it in the paper or in my phone to get a vision of how i want this part to look (i do not have a good drawing tablet, cus if i had i would use clip studio)

4 - make a gameplay that represents the song and the idea

5 - BUILD!!

I also read especific professional books to guide me through the creating process, i also get feedback and ideas from people and friends.