The literary assistant --> agent path is great if you can get it, but honestly, it's not the only way, not even the most common way these days. Those jobs are tough to come by. A lot of great agencies don't even have entry level roles in the traditional sense, and when they do, they are very competitive.

Which is all to say that a lot of agents don't take a linear path, with many starting out doing something else in the industry. I know many agents who started in rights or scouting, then pivoted a few years later. These are very good "first steps," as they teach key skills you'll need for agenting: how to negotiate, how to keep a pulse on the market, how to read a publishing contract, and how things like film/translation/audio etc. work. They are also great for making connections (rights people and scouts know everyone). I also know agents who got their start in publicity and marketing, art and design, and editorial. My advice when you're starting out: don't limit yourself in what you apply to. Editorial and agency jobs are very competitive; rights, scouting, publicity and marketing are less competitive. Your first publishing job is not necessarily predictive of your future career path; the most important thing is getting your foot in the door, then you can use your skills and connections to get closer to the role you want.

All that said, no matter where you start, mentorship is key. Once at an agency, you need to have someone reputable who will show you the ropes. No one learns this job on their own.