@BigTony I'm not super experienced but I try to make it a room at a time. Walk into the room, and move through it, fight the enemies. It should flow and feel good. An organic process of iteration. Ultimate Doom Builders feature that lets you launch+spawn in arbitrary positions helps a lot.

There's this guy I've watched when learning Quake mapping, he has his own workflow where he sketches it out first. I don't do that because of my iterative gameplay-driven process: https://www.youtube.com/watch?v=ljkv3R3P0pA