Help becoming a DM

[Andezzar]

I tend to start a campaign with a faint idea of what could happen, improvisation is your greatest friend.

QFT. Cheat sheets with names and stuff also help.

Most of the npcs you flesh out will never be met and you'll have to make up many on the fly

It depends on the scope of your NPC building and the type of campaign. If your setting revolves around a couple of characters in a small area, you are likely top use most if not all of them. If the PCs have lots of options for running around the effort to flesh out all possible NPC seems pretty tedious.

I had a DM once that put a lot of effort into world building (maps, history etc.). He did a lot of great work, but the problem was he tired to, or at least that was my impression, show off all his work which led to very restrictive gameplay. So in the end he did a lot of work a lot of which the PCs did not discover and the players did not have an experience as enjoyable as possible.