Twitter is a marketing black hole. If you write (and you do) and and tweet about writing using writing-related hashtags (and I’m assuming that you do), then most of your followers will be fellow writers, not readers. Basically, marketing on Twitter is selling to other authors who are only there to sell to you.
I’m in the same position that you are. So far, the vast majority of what I’ve sold (only 17 copies) has been from personal connections...friends, direct emails via the project panel, etc... .
I’ve added some fan art to my page to spiffy it up a bit and am working on a simple book promo video, but there’s still the issue of driving eyeball traffic to the page in the first place...
*cough*
http://shift.greatscifi.space (forwards to inkshares page)
*sniff*
*wink*