Did you Google to find out first? You should have come up with millions of suggestions just from searching the web. It's important to research and always do homework as much as possible. and if your book is already out then you must remember you don't wait until the book is out to start promotion. Promotion should begin months before the book is released. I get the feeling you have self-published? If so, you're gonna need some very, very clever ways to promote your book if you expect it to sell.
The truth is there are no "unconventional tactics that work". Sorry, but no matter what you do there is never a guarantee your book will sell and sell well. Now if you are traditionally published it's much easier and more doors are open to you for promotion. If you self-published it's gonna be challenge after challenge. The most important thing is scoring book reviews and do as much online marketing as possible. I don't know if you're a traditionally published author or doing it on your own but if you have self-published there will be less opportunities for promotion unless you spend some money or write nonfiction. Nonfiction books are easier to promote even if you're a SP author. If you wrote self-published fiction, then all I can say is good luck and do all you can to get promotion.
I can tell you what people think work and have no effect whatsoever on readers:
1. Flyers and bookmarks. Unless you're at signing or festival, these do nothing for readership. Most times people throw them in the trash and never get your book.
2. Sending out mass emails and spam. A lot of self-published authors believe this is the best way to promote and the only thing it will do is get your email blocked. I've been spammed by self-published authors tons of times and even had some who had the nerve to send me an attachment with their book! No one reads mail from folks they don't know and they are not going to buy a book from a spam email.
3. Spamming social networks and sites. Remember, you never want to spam.
4. Book trailers. They might be entertaining but they don't necessarily sell books. I know one has never interested me enough to buy a book and there are some many authors with them now that it's like a bandwagon thing.
If you're doing this all on your own I suggest you get some books on promotion. You should also be able to find things online to help you.
Promotions is a favorite subject of mine, and I agree with Stacy-Deanne, that it's one hard nut to crack. Many times the self publisher can do everything right and not sell books. I've experimented with many promotions, and the one thing that is for sure is, the writer/publisher will need to spend money. Lots of it, and stay at it. And even then, won't see any real progress for at least a year. I think one of the biggest mistakes all writers/publishers make is, they fail to say their book is a good read. I have no problem with saying that about my latest novel, "What Goes Around" - https://www.createspace.com/3411878
It truly may be one of the best books you've read in a good while. It's a ten dollar gamble and offers you the chance to become closely acquainted with me, the author, who may more than willing to help you with your future books. It's not often one can acquire help and loyalty for such a small price.