01
What it is
A written plan of the systems your business needs, in what order to build them, what each one replaces, and what it costs to run once it exists. It is a document you can act on, hand to another developer, or use to say no to the next piece of software somebody tries to sell you.
Systems fail more often on order than on quality. A CRM bought before anyone agreed what a lead is, or stock software bought before the counting was fixed, will be abandoned no matter how good it is. Working out the order on paper costs a fraction of finding out by building, and the wrong order is the most expensive mistake in this whole catalogue.
The plan also gives you a way to say no. When somebody sells you a tool, you can check it against a document that already says what the business needs and when. That is worth more over a couple of years than the plan costs, and it works whether I build any of it or not.