Remember that a thesis is you controlling statement for your essay. It is essentially the complex sentence that states your argument and typically appears at the end of your introduction, however long that may be. It helps if you use the language of your prompt or question to generate your thesis. The thesis should contain several things and can be pretty formulaic for you, working with anything in your English class:
1. Your intro should have introduced the author's full name already; come back and state the author's last name in your thesis.
2. It might help if you restate the title of the work, just as long as it isn't redundant / repetitive.
3. The thesis needs the concept you're discussing (for you this is the imagery of blood and darkness). The concept(s) has to go into this statement. That way you can be sure that you are answering the question or prompt.
4. Finally, you need to answer what I call the 'so what?' part of the concept. This is your position, what you are arguing; and is essential. Shakespeare uses this darkness and blood imagery: so what? what is he doing with this? how does this connect to a theme or bigger idea?
*all this is one (no more than two) sentence*
So, for example: if I were to write one on Macbeth and the use of nature imagery (the moon, rain, falcon, etc...), it would sound like this, given the formula above:
Through the use of the imagery of the moon, rain, and animals inMacbeth, Shakespeare connects nature to the spiritual and divine elements of the play.
I have title, author, concept (nature), and the argument I have to make in my essay that nature connects to the spiritual and the divine. I have even set up and organized my essay into three parts--the three aspects of nature, where one section of the essay will be devoted to each, consistently coming back to explain how this connects to the spiritual or divine.
So now you have to do the same thing with blood and darkness. The thing to think about is the connection to an argument. He uses blood and darkness: so what? What's he saying about human nature? about violence in man? about Macbeth's treachery and tyranny? about secrets and deceptiveness and manipulation. Use one of these bigger ideasto develop your argument to go in your thesis.