The blurb for your book is one of the most important marketing tools.

This is what's going to go on the back cover of a paperback in order to entice readers. It's also what will be displayed on e-book platforms, such as Amazon and iBooks.
You have various options when it comes to obtaining a blurb. It is something that you can choose to create on your own or you can have a third-party create it for you.

Write the Blurb

One of the first options is for you to write the blurb yourself. You are the author of the book and therefore you know more about the story than anyone else. It will ensure that you hit home the most important aspects of the story, including any conflict that you want your readers to know about.
The only downside to writing your own blurb is that you may be so invested in the story that you don't know how to condense it down to only a few hundred words – if that. Sometimes, less is more – and the blurb is one of those instances!

Ask a Reader

If you have had a beta reader involved in the development of your story, you might want to ask them to write the blurb. Especially if they are also a blogger, you can be confident that they know how to write and know what it takes to create an intriguing blurb. A reader might also feel extremely privileged for being asked – and they will do some additional promotions for you after the book is published.

Ask a Reputable Author 

Authors write blurbs for each other all the time. If you know a reputable author, such as an award-winning author or one who has hit the USA Today or New York Times best-selling lists, you might want to ask them to write the blurb. This might be something as simple as a long quote as to what they think about the book. The added benefit of this is that you will get to list their name on the book, which can add credibility to you as an author.
If you have several author friends, you might want to offer to write their blurb for them. This way, the two of you can trade back-and-forth each time you publish a book.

Hire a Third Party

You also have the ability to hire a third-party to write your blurb. This is a service that is becoming more and more popular. Essentially, you are paying someone to read your book and then create the blurb based upon what they feel is the most important aspect for readers to know. While it is an added expense, it is sometimes worth it because the blurb is such an important part of the publishing process.
It's often a good idea to have multiple blurbs created. This means you might want to write one, ask a reader to write one, and have a reputable author write one. Then, take it to your readers or ask a few close friends to read through the blurbs and choose which one they think will be the best one to hook people in.
The blurb is pretty much locked in stone once you publish into paperback. However, you may want to change the blurb that you have in the various e-book platforms from time to time. If you find that e-books sales have dropped, change to one of the other blurbs you have. This might capture the attention of other readers in order to stimulate your e-book sales once again.