A mix of studying fundamentals and just trying things even if they don't work out as planned by the end. Making a mental note on what you would like to improve on next after every piece helps. Self-critique. I'm happy many people consider me to be skilled but in my mind i'm still lacking in very many things. I think it just came gradually with time and experience, i've been drawing for many, many years. But if you have the opportunity and resources to improve quicker you definitely can if you put in the mileage!

I suggest making a study plan if you're serious on it. Kind of like school but you should schedule it around the rest of your daily routine. I set aside at least 30 minutes to a couple of hours to fundamental studies before I dive into drawing for fun the rest of the day. As long as I was able to put that time in, it will add up in the days and months, you'll see improvement for sure if you keep checking. No pressure though, not everyone has the opportunity to dedicate themselves to this so set your growth expectations realistically and you should be fine.