I've been getting Steve Slaunwhite's newsletter, For Copywriters Only, for quite a while now, and I wanted to recommend it to my fellow freelancers.
Of course, like any marketing newsletter, it's also a sales pitch — Slaunwhite uses it to market his writing courses. However, he's not pushy about it, and the value of his advice makes it well worth it to be on the mailing list.
For example, two newsletters ago he offered some advice on how to earn more: Charge for the tasks you perform that are related to the client's project, but not really part of the writing. For example, if the client doesn't give you the keywords for their SEO website copy or content articles, quote them a fee for keyword research. Likewise, if the client wants to pick your brain on website design or layout, marketing avenues they could take, etc., charge them for your time as a consultant.
I think these are great ideas, and make a really important point: Writers often view these things as part of the writing process, when in actuality, they are services that other companies out there are charging for. So rather than doing them for free, or refusing to do them at all and sending your client's money elsewhere, take advantage of the opportunity to earn a little more per project.