There is not much you can do to avoid a steep learning curve and you will feel more incompetent than an intern on their first day in the very beginning because there will be many details you'll have to manage, but unlike intern year you'll be expected to have an answer and there is no senior to turn to for help. But everyone goes through that, so it's just a matter of figuring it out during your transition to fellowship.
I would make sure your personal life is in good order as you have already because, at least at my program, there wasn't much time for personal life first year. And if you want to read something, a book that I didn't read but I wish I had in the beginning of first year is Cotton's Practical Gastrointestinal Endoscopy. I looked at it recently and it looks quite useful. If you can get your hands on ASGE videos those are very useful too.
