I think most things in life require persistence. When it comes to marketing (and whatever your marketing choice) for your book or business, you have to do one key and important thing: be persistent. We're going to call this the "persistence factor" or PF. The PF influences your success quotient. PF is directly related to the degree of success. There! Your math quotient for marketing. For those of you who hate math, let's just speak in plain English.
You cannot do these things and succeed with your marketing programs:
Irregular newsletter: if you're going to write a newsletter, be prepared to WRITE it. I like to do mine weekly. I encourage others to do it weekly not bi-weekly not monthly. Keep your brand in front of your target audience -- that's the point. But if you commit, commit! Don't do it one week and drop it the next week. Persistence builds an expectation -- that newsletter will be in in-boxes regardless. People come to expect your newsletter, so you better meet that expectation. (Hint: business doesn't happen overnight, which also requires the PF in your efforts.)
Blog, blog, blog: if you're going to do a blog, BLOG! I do it daily (unless I'm traveling). The idea is to keep a constant "pressure" point on your audience. Keep the content rolling. Keep your brand in front of the audience. Give them a reason to come back to find new content.
The point is, keep it moving. The true bottom line: if you're going to market and market right, do it! Keep doing it for the long-term success. BUT if you're not going to do it right, don't do it all. Why? Because lack of persistence has the opposite effect: people will think you've closed shop. So once you start doing marketing on a consistent basis, stick with it.