I start with main ingredients. We have red meat once a week, chicken twice a week, and the other four nights are a mix of fish and veggie dishes, depending on my budget that week and what I feel like (seeing as I plan it all out and shop for it!).
I plan two weeks at a time.
I keep Friday and Saturday evenings very, very simple. Usually freezer food, using up stuff in the cupboards or things like omelettes/jacket potatoes. I know I won't feel like cooking on either of these days.
I try to get two meals out of one 'buy' - so split a pack of minced beef to make spag bol for one night and a chilli which can be frozen for the following week. Or make a roast chicken on a Sunday, and have chicken soup and bread for lunch or tea the next day. I'm not religious about this, but I try and spot where I can make things go further or be organised ahead of time.
I am not as organised as the posters above (no spreadsheet!), but I know what I can cook/what my family like, and will stick to that and usually add one new dish each fortnight.
Pudding is always fruit and/or yoghurt on week nights. I buy a few staples (apples/bananas), and then whatever fruit is on offer at the supermarket (so usually works out to be seasonal).