I normally wake till I'm hungry (so I'm more motivated to think about food), think about what sounds good to me, search around online for mouth-watering recipes, write up a grocery list of the ingredients + everyday staples, then go shopping.
Switching to doing this from just shopping whenever I felt like it and improvising in the aisles has led to multiple hundreds of dollars in savings. I'm sure if I also took into account per serving cost of each meal I could cut this cost down even more.