It is NSFW, but this video is jammed packed with excellent advice. How to ask for a decent daily rate, what should be in a contract, how to get paid etc.
If you are freelance or trade as a company then this 40 minutes is well worth a watch. Not only could it save you money, but getting a lawyer involved with contracts at an early stage could avoid huge legal costs later.
We know editors who have lots thousands of pounds because a client has refused or been unable to pay their invoice, so it does happen in our industry.