Facebook and Twitter are fairly useless for authors and publishers. This is not to say they should be avoided utterly, just that it does not pay to spend a lot of time (and certainly no money) on them. If one already has fans, it is good to have a presence for them, but let’s face it — a writer does not have that many interesting announcements to make. It’s not like being a musician who announces gigs regularly.
Instagram? Pretty much the same as Twitter and Facebook, it would seem. I have never used Instagram because I have neither a smart phone nor do I take many pictures. Tumblr might be a little better. Not much, but a little. It is a place one can post writing samples and that sort of thing. Again, it is more for the fans one might already have; don’t expect Tumblr to drive book sales. Pinterest might be fun but not much for promotion. I dropped my account after ‘pinning’ for a couple years.
I might just drop Twitter too. I haven’t the time nor interest to post interesting stuff there. My ‘personal account’ is supposed to be for the music career but there’s nothing happening there. The Arachis Press account has the occasional publishing announcement that is probably of little interest to anyone.
So what works better than these? I suspect an old fashioned email list might. Not sure about that but it’s one way of actually getting information to potential readers/buyers. A website and a blog are definitely important. One needs a searchable presence, a place where any interested person can find out about you, your books, your life.
YouTube is certainly useful, assuming one has compelling content to post. I’ve put up book trailers in the past (with my own music) but they haven’t attracted much attention. They were probably too long for the slide show format I used, and did not hold viewers’ interest. I will continue there, and with various sites where I can post audio (Reverbnation, etc.).
These latter are, of course, more useful for a musician than for a writer. If one is both, the two can (at least theoretically) cross-promote. Like the music? See my book. And vice versa. My niece, ‘Mean Mary’ James has certainly sold way more books because of her music (and hugely successful YouTube presence) than she would have otherwise. I should undoubtedly spend more time on music — not that I have anywhere near her level of talent!