There's nothing more scary and exciting to notebook lovers than cracking open a brand new bound notebook to break it in. I love a brand new journal because the pages are so crisp and the sensation of a brand new cover under my finger tips is lovely. I may have an addiction :) If you've chosen to journal in a physical notebook, you will be presented with a few tasks to set it up before you pour your thoughts and emotions into it. Let's talk about breaking in a journal.
When you have a bound journal, one with a spine and is oven sewn together in some way, you have a stiff spine to deal with at first. Loosening it up without breaking it is the goal. There's a very simple process to doing that and in the end you'll get a notebook that will lay flat for you to write in and won't fall apart as it ages. Ryder Carroll, the inventor of the Bullet Journal system for productivity has a brief video on how to break in a journal and it works for all bound notebooks of any size.
Spiral bound or glued notebooks don't need the same treatment in order to last for years.
After you have your notebook broken in, you'll want to decide if your pages should be numbered and whether an index is necessary. For my personal log journals I need numbered pages and an index so I create an index in the first 3 pages of the book and then with a fine point pen go through and write all the page numbers into the book. This way I can organize and sort my thoughts and important pages. My diary journal has a smaller index since it spans several years. I have just marked what pages cover what years. You may not need an index or numbered pages. Again, that's completely your preference but it's important to decide before you start writing.
Last, but not least, put your name and a way to contact you on the inside cover. That way if you happen to leave it somewhere, hopefully someone will be kind and return it to you.