This is actually very similar to a project I use in my classroom. I will give you some advice I try to give my students.
Keep in mind that as an 11th grader, you are probably expected to write questions that are of 11th grade difficulty. This means that while some easy plot questions are okay, there should be a bigger focus on themes, characters (especially examining major character qualities and changes) and critical thinking. I encourage you to think of phrasing questions with the words "cause" and/or "effect" (ie: What effect did [insert major event] have on this character? Or, What caused [character] to change from [one personality trait] to [another personality trait] toward the end of the book?).
Next, make a list of several literary elements (common to all literature, see link below for a full list). Then, as you read, make note of chapters, scenes, or quotes that utilize any of these. High school literature exams nearly always assess the ability to recognize different literary elements within the text.
Finally, I encourage you to dig out some of your old literature exams. Get ideas from your own teachers as to what kinds of questions to ask. I find myself writing very similar types of questions for every different novel I teach because literature is made of the same basic parts.
The second reference link (below) will take you to information on Bloom's Taxonomy levels of questioning. Within each of the levels, prompt words are provided. This would be an excellent resource for writing higher-order-thinking questions.
Writing a good test can be difficult, so it makes sense that you're having trouble doing it. As you approach this assignment, try thinking about each kind of question in a different way.
True and false questions focus on facts. These questions test whether or not students understood the information they read; the answers are not open to interpretation. To write a good true and false question, you should focus in on a specific detail from the book. Choose details that are big enough that anyone should remember them, but small enough to be a little tricky. For instance, you could describe (correctly, for a “true” answer, or incorrectly, for a “false” answer) the hobby of Melinda’s friend Ivy or the theme of Melinda’s year-long art project in the book.
Good multiple choice questions should make a test taker think a little harder. These questions still focus on small events in the book, but they usually require interpretation of the details as well as knowledge of the facts. As you write these questions, think about what the text says and what it means, as well as what it might mean to somebody who has not been reading carefully. Here’s one example of how to do this: In the section “Second Marking Period,” Melinda sums up a description of her winter vacation by saying, “I am actually glad to go back to school.” A good multiple choice question might ask why Melinda is glad. If you have read the book carefully, you know the real answer is that she did not get along with her parents over the holiday. Give that as an option, and then provide options that might seem reasonable to a student who has not read the book as carefully as you have. Why else might somebody be glad to get back to school after a vacation? Some kids feel idle during holidays, but Melinda was not idle during hers, so that might be a good option for a possible wrong answer choice. Some kids look forward to seeing friends at school after the holidays, but Melinda is an outcast, so that would be a good wrong answer choice as well.
Short answer questions usually take even more interpretation, and they focus on ideas that come up over and over in the book. Unlike true/false and multiple choice questions, these can have an element of the student's opinion. Ask questions that start with words like “how” and “why.” For example, you could ask why Melinda avoids mirrors in the book or why the author, Laurie Halse Anderson, chose to call the book Speak. Check out the eNotes description of the book’s themes and characters for more ideas.