Perhaps someone else is using the materials you have planned to use. Perhaps you have pursued your plan to the very end. Just grab some likely looking titles and start looking in them. It's a good idea to write down the citation information, author, title, publisher, etc., for future reference. But don't misuse that information.
Some genealogists are so concerned with efficiency they never want to research the same book twice.
So they note the book in their research log and are reluctant to return to it. Again, I'm a bit unorthodox. I find it's sometimes helpful to travel the same road twice, or even many times. On occasion, I've even paid a professional genealogist to follow in my tracks and see if I've missed anything. Conversely, on important matters I sometimes stalk a professional researcher's trail through documents to ensure they haven't missed something.