Education is a wide discipline with many areas to inspire research. Using background resources, like encyclopedias, handbooks, or some other books and websites can show you different directions your research might take.
Think about why you enjoy teaching or the topics that inspire you to become a better teacher. Research is often more enjoyable if you investigate something that matters to you.
Background sources are also helpful to understand how other people (including researchers) might talk about your topic, which gives you additional ideas for search terms.