[Laura Lond]

There are several ways, you can offer your book on LibraryThing, for example. It worked great for me. Or you can announce a giveway on a blog - yours or someone else's.

 

[Laura Lond]

If you do it through LibraryThing, they'll take care of it for you (that's what I love about them). You just need to post the info about your book, upload the cover, and mention how many copies you are giving away. People will start signing up, and in the end LT will provide you with email addresses of the winners. Then you'll just email them the file.

 

[Laura Lond]

A few more questions: what is the best duration for the giveaway? 1 week? 2 weeks? 1 month?

The duration is up to you, you can make it a week, two weeks, etc. You also choose whether you offer a paper book or a printed copy. As far as I remember, on Goodreads it has to be a printed copy. With LibraryThing, you can do both.