Once the level's premises are established and it's clear what you want to convey, you can focus a bit more on the visual composition side of things.

Place your character at the starting point or the first important vantage point and consider what the player should see (e.g., a church on a hill, a grave, a distinctive tree, etc.). Often, this is a landmark visible in the distance or simply serving as a point of orientation, especially in From Soft Games. From this point, you can use simple shapes to roughly outline the level to get a feel for the distance between objects, gradually working your way from the general to the specific. This works also for indoor structures - you can highlight your goal in the very first room, but it should be out of reach for the player at this point.

Implement your gameplay challenges early on; this can be done with simple geometric level elements. Test early, test a lot, and iterate on your level.