This is the moment of truce in your research when looking for information about your topic.  First you need to start off with your inquiry question and it is best if "little words" like "on" and "of" are kept out of the sentence.
An example regarding my last post on clothing trends: What might explain why clothing trends change every decade?
Also, words that are good for key searches for later are a good idea to fit in.  Such as from above, I could use the words clothing, trends, clothing trends, or different variations in my search.

The next step would be to find a primary purpose in writing.  Think of some a questions that you could ask about things that interest you that could help you find answers for your question.  For my example I could do more research on what were the clothing trends in certain time periods like the 80's or 90's.  I can also ask myself what other hypotheses could I make about my topic that could help me find other claims or thesis.  On the topic of clothing trends, I could ask questions on why people follow trends or how people make them.  All of those would center around the topic of clothing trends and why they would change.  You can also consider any thoughts or assumptions you have on your chosen topic, like the trends I follow myself or what I think of people's clothing in different decades and if I would follow them too.
This process may take awhile to think of your final question but write down as many ideas as you can to get your brain thinking.