1. Point to a paragraph (page number) from the book or one of your research materials that supports your thesis.
2. An argument you can make that supports your thesis.
3. An argument someone else makes, that doesn't support your thesis, but for which you can point out holes in their reasoning.
4. A list of examples that support your thesis.
5. A list of counter-examples that argue against someone else argument that your thesis is false.
6. An experience or anecdote that supports your thesis.

Now once you have decided on an idea, expand it into a paragraph or two. The book "Ways of Writing" by the PSU Writing Center suggests several ways to generate ideas. I repeat them here for your convenience.

1. Listing It is exactly what it sounds like. Every assignment and every thesis, could go in many different directions. Before picking one, list as many as you can think of -- just write them down as fast as you can. After a bit, circle the interesting or important ones. These may be the basis for your supporting paragraphs.

2. Clustering If you're a visual person and feel constricted writing paragraphs, try clustering. It's like free association.Write your main idea down in the center of your paper and draw a circle around it. Now quickly jot down ideas around your main idea, and draw circles around these too. Then put down any ideas that seem related to those ideas. Some clusters of circles will probably end up with more ideas than others -- this might indicate the direction your paper could go. When you're finished you will have a visual map of your ideas.

3. Carding If you are a kinesthetic learner, try index cards. Write an idea on a card, and then write another idea on another card. Keep going until you run out of ideas or cards. Go through your stack of cards and write something new about each previous idea. See which ideas change or develop. Spread out your cards and sort your ideas into stacks. Some ideas may be related; others may be irrelevant. If you are working on a research paper, this is a good way to sort through quotations you might use.

4. Free writing Just start writing. Don't censor yourself. Just keep your pen moving no mater what comes out. Don't struggle to produce a perfect sentence and don't worry about spelling or punctuation; just write whatever pops into your head, even if it seems silly or off topic. If you get stuck, write "I'm stuck" until a new thought occurs. Try writing for 5 or 10 minutes. By freeing yourself up in this way, you will be able to get many of your ideas on paper, and afterwards you can decide which ones you would like to explore and expand.

5. Looping After a 5 or 10 minute free write, try and identify the most important or interesting sentence you've written, and circle or highlight it. Rewrite this sentence at the top of a new paragraph and free write again with this sentence as your starting point. This is a good way to explore your ideas in greater depth or detail without the pressure of more formal writing, and you can repeat the looping exercise as many times as feels useful.