How do I write my thesis properly?

No matter what argument you are trying to make about this text, you can approach writing a thesis statement this way:
First of all, select a subject that is interesting to you. For example, in David Sedaris's Me Talk Pretty One Day, you could select the subject of his childhood or his habit of using exaggeration as a storytelling technique.
Next, select a literary focus that concerns a topic or term you have learned about in class. Sedaris employs hyperbole and irony in this particular collection, and either one would make a great literary focus for your thesis and for an analysis proving your argument.
Finally, choose a verb or a verb phrase that brings your subject and your literary focus together. For example, you might be able to create something like this thesis:

Sedaris's descriptions of his childhood reveal his ironic sense of humor in surprising ways.

The subject, which is the descriptions of his childhood, does something interesting for the literary focus, which is his use of irony. Basically speaking, your thesis sums up interesting idea for your reader. The rest of your essay will need quotes and careful analysis to prove your thesis, but you will be well on your way with a simple and clear thesis written according to this easy formula. Good luck!