Not saying I do all these, but in principle:
if you don't already, do a meal plan a week ahead, so you know what you need to buy and what you are going to make each night.
If you have a freezer, always make double of things so that at least one night a week you just have to take something out in the morning, and reheat in the evening.
Make a job lot of bolognese sauce, which you can turn into lasagne, chilli, shepherd's pie as well as spag bol.
Buy a calendar with a column for each child and adult so you can note down appointments/activities/parties etc.
Buy birthday cards in bulk; buy birthday presents when you see them on offer.
Lists, lists and more lists!
have a list of what is needed for which days (homework/PE kit/stuff for after school/CM activities) Hang it in the kitchen or by front door and get stuff ready the night before, no matter how tired you are (def don't do this one anymore, note to self to start doing it again!)
For annual things like Christmas/holidays, keep checklists on your computer, then you just need to update each year rather than start from scratch.
Have a note book, jot down to do things as you think of them.
Got to go out now, will see if I can think of any more (it's reminding me that I used to be organised once and need to get back to it!)