You need a topic
To start with, what questions have other historians asked about your general topic? If you are writing about something that already has been addressed by other historians, it can be very useful to survey that literature and ask yourself which approaches are interesting to you.
And remember: history is about change over time. Simply describing the events of the past isn't very interesting, unless there is disagreement about what actually happened.
Use Articles+ to find Book Reviews. A good review identifies the scholarly debate in question. If you have a book you like, quote the title in Articles+, then limit by "Book review" in the Content Type options on the left.
In your junior seminar, you'll be introduced to many different ways of writing history. Some approaches have a long history of their own, like biography and the history of nations. Others are new, like transnational history or the study of race and gender in history. History has established subdisciplines, with their own ways of thinking about particular questions. So think about what you are interested in:
Do not choose a topic for which there is no secondary literature and no primary sources that are accessible to you. Some questions to ask yourself, your advisor, and me: