Giveaways can be a riot. I usually pic three prizes: Book/ARC, bookmarks, and a trinket I've made. Last time it was a zipper pull.
All prizes must be able to be easily mailed. Books/ARCs can be shipped directly from a publisher. Where bookmarks, and trinkets will be up to you. If there is a border (like in my case), make sure there won't be a problem sending your prizes to your winners.
To encourage entries, add the giveaway link to your blog tour stops, cover reveals, and anyone that is willing to post it.