A good thesis statement for any book begins with the theme. There are many themes to choose from in The Giver. You might choose the triumph of individuality, the importance of memory, the celebration of difference, or the tyranny of suppressing choice. Once you have chosen your theme, write a sentence about it. Your sentence can simply state the title and author of the work and the theme. For example:
An important theme in The Giver by Lois Lowry is that memories make us human.
Then you go on to write your essay!
These are fairly strong topics upon which to write a paper. I think you might want to streamline some of them to make them about the characters in the text. For example, let's take the first one. In The Giver, Utopian visions of the good are difficult to embrace because different characters voice multiple conceptions of perfection. I have always felt that in writing thesis statements about texts, it is essential to link the development of a thesis to characters in the work. For instance, in the last one, I would try to link characters to this idea and prove that as it will be a more coherent work. Instead of the personalized, "you," why not, "characters in Lowry's work are challenged to find true happiness devoid of struggle and pain." This keeps the writing more streamlined, focused on the text and the characters. I hope some of this helps.