Think about the transferable skills you can bring to the table; feel confident about the fact you’re coming from a different industry or different part of the media industry because you will be bringing a whole new and interesting perspective!
Try to learn about every aspect of publishing, not just the department you think you're interested in. This will be crucial in giving you an overview of how the publishing machine works as a whole.
Wander bookshops! The best way to learn about your new industry is by getting acquainted with the market. Regularly going to bookshops (or in the event of a pandemic, their websites!) is a great way to see what’s selling & the trends in the market with covers, titles, copy etc.
Read broadly, get to know your own taste and where this does - and doesn't - intersect with what's working in the market.