This week, I'm going to get more specific about things that I've learned. Again, I should emphasise that the only experience I have is my own, so don't sue me if you embark on a freelance life and end up in penury.
First thing, and this is boring: get an accountant. It helps an enormous amount. But make sure you understand your accounts as well. There are tremendously useful software packages out there that will help you with that - and the most common worry I hear from fellow freelancers is uncertainty about who you owe, what to do about VAT etc. If you do a bit of work on that, regularly, life will be easier and you can free yourself up to worry about important things like the lack of work and impossibility of paying to repair your boiler.
Also, think hard about becoming a limited company. Some clients might insist on it, your accountant may well suggest it because it can save you some money, but it adds considerably to your administrative overhead. The extra money might not be worth it.
Second thing: get over any qualms you might have about discussing money. All that discrete muttering about salaries will go out of the window when you're a freelancer and your cost will be discussed like you're any other piece of equipment for hire. And you should be similarly clear and unequivocal. You'll be surprised at the number of people who'll ask you to do speaking gigs and the like, assuming you'll do them for nothing.
If you're not very clear about assumptions, you might find yourself doing unexpectedly unpaid work. Ideally, you should probably get commitments in writing and in advance, but I have to say I've never done that and I've only been let down once.
Third thing: think about when you'll get paid. Most large organisations are fine and prompt payers. In fact, US businesses worrying about Sarbanes-Oxley seem mad keen to pay you as soon as possible.
But agency accounts departments have spent long years earning as much as possible from billing early and paying late and they tend to pay only when ordered in triplicate by the deceased founder of the agency. You have to get used to chasing them. Just as you'll get used to booking your own travel, doing your own photocopying, buying your own coffee and putting your own biscuits on little plates to impress clients.
But, look, I've done it again. Out of words. Next week - more money and learning.