The easiest and cheapest thing you can do is start with some dry firing. Buy some dummy rounds and practice loading/unloading the rifle, cycling rounds, manipulating the safety, adjusting sights, etc…. This way when you get to the range you aren’t wasting your time on simple tasks.
When you go to the range always shoot for accuracy, not speed. Once you master accuracy then you can work on speeding your shots up. So many people start shooting fast and then try and work on accuracy later, it doesn’t work that way.
Now that you have the basics of how to handle and fire the rifle you can work towards more advanced skills, like clearing jams, tactical reloads, etc… I would recommend doing lots of reading and watching youtube videos. Its free and gives you an idea of where to get started.
Finally you can start taking classes. I recommend this for last as you need a good skill base prior to attending to take full advantage of what they are teaching. Classes are usually expensive but are well worth it and you will likely learn more in 1 class than you will with months of reading and watching YouTube videos.
My last piece of advice is as you build your self-defense setup, take into account what fits YOUR needs. Just because law enforcement use a certain caliber of firearm or navy seals use a specific light/laser doesn’t mean its right for you. Defending you home and family is very different than hunting down the Taliban in some desert third world country. Oh and don't forget physical fitness. The best guns and gear are worthless if you break a sweat getting off the couch to walk tot he fridge.