How best to market your book depends on a number of factors

What you enjoy doing. That may sound silly. Why would you bother making a book trailer – even if you enjoy doing it – if you don’t believe it will promote sales of your book? Well, it can’t hurt, so why not? Anything that gives you pleasure is energizing. Your positive state of mind is your best resource. Watching that really cool trailer you just uploaded will likely send you back to the computer to write. For the same reason, try to avoid doing things you hate. There is of course some tedium that can’t be avoided – for me that was begging for reviews – but try to keep it to truly necessary things. Your default response to doing things just because other authors do them should be No. But, hey, if you are outgoing and enjoy meeting new people, so arrange some speaking engagements, even if they’re just small gatherings in local coffee shops. Perhaps none of those coffee drinkers will buy your book, but you’re still likely to bring a lot of good things away from the experience.

The kind of book you are writing. Things such as genre, whether it is part of a series, or whether it’s the only book you currently have for sale will affect how you promote it. Does the plot revolve around a topic regarding which you could offer “extras” on your blog? Are there magazines about this topic that might be glad to print fillers from you? If so, things make sense for you that don’t for me.
Genres differ greatly. If you’re writing a romance, the good news is that the market for them is insatiable. The bad news is that everyone else in the world is writing romances. Even giving yours away is hard; you have to compete with a lot of other free titles. The same is true, in smaller numbers, of mysteries and thrillers.
I suspect genre may have been to my advantage. I have twice advertised Book 1 on BookBub, where there are a lot of subscribers who are fans of historical fiction. Luckily for me, relatively few historical fiction titles appear in their newsletter. I also had the advantage of writing a series, meaning I could make Book 1 free (first during temporary promotions, now permanently), leading to sales of Books 2 and 3. Even if your books aren’t a series, but you have more than one for sale, you can use a discount or free promotion of one to attract readers to the others. If you are publishing your first book, it’s a hard go. Your best marketing strategy is to lower expectations and put your time and energies into your next title.

Your skill set and budget. Unless cost is not an issue for you, your default response to spending money should be No Thanks. Don’t let go of a dollar until you are convinced it is reasonable to expect the expense to yield results. Look at every dime you spend as money you will never recoup. You may be pleasantly surprised, but the statistics are not encouraging. The vast majority of authors sell very few books. So DIY as much as possible. Barter services with other writers. But do spend what is necessary. If, like me, you can’t put together a professional looking cover, then shell out. If you can’t swap editing services with writer friends (like I did), then pay for it.

It’s easy to fall into the trap of throwing good money after bad, bombarding your frustration with dollars. After you subscribe to blogs for writers, join writers’ groups, etc. (as you should) you will begin to receive sales pitches for everything from books on self-publishing, software that will write your book for you, tutorials on how to use that software, “a feature spot” on a blog, contests you can enter (at a price), prizes you can be nominated for (at a price), and on and on.

I’m not saying that all these things are without value. You need to buy and read a few books and some of the other things would be nice to have. I recently watched a well done webinar that was selling a tutorial (probably equally well done) on how to use Facebook ads. I would be more than happy to take such a tutorial – if it didn’t cost over $1000. When the guy decides to put his advice in a book and sell it for $10, I’ll buy it.

Don’t buy anyone’s claim that their book, tutorial, webinar, online course, or whatever guarantees success. A lot of boring, badly-written books get published and flashy Facebook ads aren’t going to turn them into bestsellers. And it’s an unfortunate fact of life that some fascinating, well-written books will never appeal to more than a small audience. Marketing tricks might give a book a temporary sales spike, but if there isn’t a real, enthusiastic audience out there, it will quickly flatten out.
I’m not saying you don’t have to advertise to get exposure. Of course you do. I am saying you should adopt a healthy skepticism. My books have sold in the thousands, but I don’t believe clever marketing tips are going to turn them into NYT bestsellers. Only readers loving them and raving about them to their friends could do that.

So don’t sucker yourself into thinking, if I just do that, if I just spend this much more . . .
Also . . . Interaction with other self-published authors yields many rewards, but increased book sales are not among them. Don’t delude yourself about that.

Don’t feel you have to be active on every new social media site. A blog, Facebook, and a presence on Goodreads are quite enough time to spend on the Internet. If I ever choose to be active on Google+, Twitter, Instagram, Pinterest, or join Facebook and LinkedIn writing groups, it will be for my own enlightenment and enjoyment and not because I’m dumb enough to think it will sell books.
Don’t drive yourself nuts trying to create a “brand.” I admit – on this point I am a minority of one. All the experts say the opposite – creating a brand is a must. For me an author’s name is their brand. If I like one book they’ve written, I’ll look for another. If I didn’t like it, I’m unlikely to try another, no matter how cute their logo is.