I started vaguely planning my meals by the week sort of by accident. A friend made me a "weekly planner" whiteboard that had a "menu" section I thought would be totally useless.

But I started jotting down some ideas there, just on a whim, and I'll be damned but I love it!

I don't always follow my own plan, and I often just write the main/protein part and wing it a bit, but it's great having at least an idea what's coming down the pipe for the week, so I can actually plan prep and shopping, and use up what I have. It looks something like:

MON lentils
TUE beans
WED tofu
.... 

Etc, so like now I know to soak beans overnight on Monday, and go buy tofu before Wednesday.