How to promote your book (without giving up writing)

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Stephanie Cowell, a wonderful novelist (click here to see her titles), wrote to me this morning:

I keep up my website and blog there, keep up my art web site, keep up my Amazon page, twitter, Facebook, reconstructing mailing list (!), answering many lovely e-mails….  What else do you do? I am afraid if I try much more I will not be able to submit my next book for hopefully a contract late winter. I'd appreciate advice. I also have not scheduled many in person signings. This is all so much...