I start with weekend meals - I enjoy cooking and like to spend a bit more time, making something which either takes longer or feels a bit fancier. Don't get me wrong, nothing cheffy at all. It might be a lasagne with a properly made, slow cooked beef ragu, for example. Weekend meals are usually meat-based too. Then, I'll look at my shopping list for those meals and work out a weekday plan based on the leftovers - possibly a bit of leftover meat, almost always lots of veggies, and then decide on any supplementary shopping needed for those meals. I try not to buy any additional meat so weekdays are mainly veggie, unless using up meat from the weekend.
In the summer months, I try to make a (typically mumsnet) massive salad, which does two nights with some variation in toppings or sides. In Autumn/Winter, I'll aim for a big pot of soup most weeks, which again does two nights.