I got a really unexpected amount of hits on my post about essays the other week, so I thought it would be helpful to write a guide to something else I know people have a lot of trouble with: thesis statements.
Thesis statements are kind of complicated things. The only reason I'm any good at them is because my teachers in high school constantly drilled us on them until we more or less understood how to go about them.
I'm no expert, but these are some guidelines-- specifically for English essays, but they can be tweaked to fit any topic-- from what I've gathered over the past four or five years.
1. You don't need to include the title/author/genre. In general, most teachers expect that to go in the introductory paragraph itself, so there's no need to try and cram it into the thesis statement.
2. Your thesis statement should only be one or two sentences long. Ideally, your intro paragraph will set up the context for your argument; that way, the thesis statement should be the heart of what you're trying to argue. It generally goes towards the end, or as the last sentence of, your intro paragraph.
3. Your thesis statement should be specific, but not too specific. If that makes sense. You want your thesis statement to be specific enough that what you're arguing is clear to the reader, but it needn't be much more specific than that. The actual narrowing down and elaborating on your evidence is where your body paragraphs come in.
4. Your thesis statement should connect to the topic sentences of your body paragraphs. I don't mean that you have to literally use each topic sentence as an elaboration on whatever points you mentioned in your thesis statement, but it should be clear that they are relevant to each other. A lot of people use topic sentences as a means of jumping right into the argument when they should-- at least from what I've been taught-- be used to show how the topic of the body paragraph will relate to your argument/thesis statement.
And then you use the rest of the body paragraph to back up that claim and elaborate on your argument.
These guidelines have generally worked for me for any kind of essay. If you're not specifically writing about a book, you can skip #1, since title/author/genre generally only applies to analysis of books in English classes.
If you're looking for examples, Google can probably be of assistance. If you give me a topic in the comments, I will also consider giving my own example of what I think would constitute a good thesis statement (provided you're not just trying to trick me into doing your homework for you).
Hope this helps!