Does Book Promotion work?
Yes and no. Yes book promotion works, however, it only works for a short time, unless you book is something extraordinary. Therefore, book marketing/promoting is a constant thing.
One of the biggest things in promoting books is to establish your readership. You establish your readership by writing more books.
Once a readership is established, those readers are waiting for your next book. Those same readers will blog about you, tweet about you, and tell their family and friends about you. Slowly, but surely, you will grow in popularity and your readership will increase.
Just remember that before your publish your book, make sure it is the best you can possibly make it: proofread, revise if necessary, hire an editor if necessary, etc.
No one wants to read a book that does not flow well or does not have a plot going anywhere.