It's a long journey, and the different skills build on each other constantly. If regularly switching focus on what you're studying works for you, do that. No need to stick absolutely to a specific course, unless you find that helpful. (sticking to self-imposed rules can help with discipline for some people, for instance) I second in-person classes/workshops. I find they really help with motivation and accountability, even when there is no actual assigment to turn in. For instance, if I'm at a workshop and I'm the only one not drawing, I kind of feel bad for not participating. Everyone, whatever their skill level, is making an honest effort, and I would just rather stare at a blank page than try something? Nah, not happening. Plus, you're less likely to get distracted than at home, and you can ask for direct feedback and advice from other artists. Drawing from real life requires adaptation, but I'm sure you will be able to do it if you keep trying and improving. Same with drawing from imagination, although a better understanding of the actual construction of different objects will greatly help with putting your ideas on paper. In any case, the main goal is to keep drawing. The best way to achieve that and what your practice should look like depends on who you are. (what motivates/demotivates you, your goals, etc.)

Sounds familiar. I had art classes as a child and some drafting classes in college, but it had been years, decades really since I had put any serious effort into drawing. In 2021 I got the urge to start it up again. I started watching videos, bought some supplies, books, even read some of the books but like you it was sporadic. I'd get going but then stop, often for months, maybe as much as a year sometimes before I'd get going again. Last year was my latest attempt and so far I've been sticking with it. After finding myself watching more and more Proko videos, last August I finally bought the Drawing Basics course. At the same time I signed up for an Intro to Drawing class at the local Community College. The Drawing Basics complemented the in person Intro to drawing class nicely. I've followed up the college class with a Figure drawing class and am now starting a Portraiture class. I'm currently doing the Proko Portrait Drawing Fundamentals course while I take the college Portraiture class. Although this is just the second week of the class, I am again finding that they complement each other rather than being redundant. For me I think I needed the structure of an in person class to get over the hump. I've got a bad case of SQUIRREL!!!! so having a set schedule where I will sit down and draw a few hours a week, and then homework assignments with a hard due date to get me drawing at home has helped a lot. To be honest a lot of the skill practice is boring and some of the exercises seem dumb and wacky. Some of them I still find dumb and wacky (blind contour drawing I'm looking at you), while others I have come to appreciate. Drawing is not a particularly easy thing to learn. No individual skill is particularly difficult but there are a lot of individual skills to learn, and they all seem disconnected until they aren't. Taking the Proko Drawing Basics alongside the college Intro to Drawing really highlighted that for me. Two classes with a similar intent, yet there was not nearly as much overlap as you might expect. Simply there is a ton to cover, and they chose to focus on some different areas. I've also come to believe in the saying All work and no play makes Jack a dull boy. At least for me I need to throw in something new from time to time to maintain my interest. I can practice line quality while I learn more about perspective, I can keep working on light and shadow while I learn figure drawing. I'm doing this for myself so it should be fun (mostly), it is not my job. If you are interested in perspective I can recommend Marshal's Perspective class, and he has quite a few videos available free to get a sample of it. I did buy the full course, but I've just been taking it in small chunks where I can fit it in. Another good source for perspective is the book Perspective Made Easy by Ernest Norland. It has been in print for around 80 years so it is easy to find a used copy, but even new the current Dover edition is only about $15.