I'm unconvinced that anything besides writing more and better books has much of significant impact on career/sales, and the more I learn about the business, the more that I feel that way.
Self-promotion can have a sales spike effect. Of that I have no doubt. But how big a spike? And how important is that spike in relation to the kinds of numbers involved in a successful book or, more importantly, a successful career? Take my first book. In the first six months I sold an average of 75 copies* a day every day. That earned out my advance plus ten percent.
This is fabulous and I'm delighted. But in order to have any real impact on sales (the kind of impact that would really change advances or earnings) I'd need to find something that would improve that by a minimum of something like ten books per day every day for a similar period. To have a career that will allow me to survive without a second job (which most writers have) or a spouse who is the primary source of income and insurance (my case) I would need to sell at least 150 books a day every day for the rest of my life +inflation. To make a decent living I'd need to make that something more like 300 books a day. To crack six figures it'd have to be ~800 books a day.
I would love to believe that I could come up with a self-promotional effort that would have a several hundred books per day kind of impact on my sales and that wouldn't eat up so much time that it would counterproductive in terms of producing the next book (or preferably the next several books).
However, I'm pretty sure that if I take the same amount of effort that kind of promotion-driven sales bump would require and apply it to writing, I can produce a complete extra book (or even two). Given that the best promotion that I know of is to have another book come out, one that's as good or better than the last one, that seems like a simple bet. Especially when you consider that in addition to a new book's impact on backlist a new book generates its own sales to add to that per day number, and it will hopefully help me build a personal brand as a fast reliable author (both with publishers and readers).
So currently that's where I'm focusing my main effort--writing spec books in the gaps between contract books. Will it work better than all the other self-promo stuff? I don't know for sure, but I personally find writing more books both more rewarding and more quantifiable than any other promotional effort I could engage in--I love writing, that's why I do this.
Of course, that's not going to be everybody's answer and I completely respect people who've chosen to do more self-promotion than I have, but it's just not my thing.
Thoughts? Comments? Questions?
*all numbers in this post are for mass market paperbacks.