The key is: What do you want in the way of advancement?
Is that to work as many games as possible, largely for the financial return? If so, just make yourself available. There will probably never be a lack of assignments for you, even if your knowledge and skills stagnate at the 3rd year level.
Is that to regularly work "prize" high school assignments (perceived or actual)? If so, you'll need to align yourself with folks working those types of assignments, and with whom you can show compatibility, so you are on their radar when the time comes. The skills and knowledge you will need to develop will vary with the expectations of those other folks.
Is that to progress to NCAA football? Now you are in a totally different universe. At that level there is no such thing as knowing enough to just get by. You must know rules backward and forward. Your mechanics must solid and consistent, and what is expected of officials at that level, i.e., you must know CCA mechanics thoroughly. But, the biggest hurdle is that you must be committed and patient. You have to be willing and able to go wherever, whenever, you must to get the exposure needed. In this day, unfortunately, that means spending a lot of money attending the many clinics that can be found in virtually every area of the country, today. And you might do that for many years, before you get an opportunity at even DII, much less FBS - if you get an opportunity at all. You must be in really good physical condition. That can't be overstated. You simply must be self-motivated to get into the rule book (and mechanics manuals). Join - or start - study groups. Show lots of hustle. Wow. There is so much more. If you can find an FBS mentor, listen, learn, and be patient.
Is that to progress to the NFL? Well, the good news is that the NFL is in the same universe as FBS, but is more like the Sun than simply a planet. In addition to rules and mechanics skills, now your judgment is really put to the test (even more than at FBS, if that is possible). This requires 7 days per week, 365 days per year video review, philosophy study, on, and on, and on. It is, essentially, a full-time job. Indeed, it is the only employment a number of NFL guys have, although most are otherwise professionally skilled and employed.
That's my nutshell for you.