I'm sure most of us know someone who, despite obvious incompetency in a self-taught art or skill, assume that they're work is that of a prodigy.
Imagine how much progress isn't being made while in this sate of mind, especially when, in hindsight, some flaws are often considered to be intentional or stylistic.
To be capable of recognizing this, and how much more capable they might be of narrowing the contrast between their own work and that of a master of their craft would be paramount.
The extreme of this is called the Dunning-Kruger effect, and those that are afflicted by it are going to have a hard time overcoming it alone considering that they do not or can not look at their work realistically, with honest criticism, and often cannot even use the criticism from others effectively.
There is obviously much more variance between this and being clairvoyantly aware of ones skill, but I think that even the average person would benefit greatly from being hard on themselves when trying to teach themselves just about anything.
Recognizing contrast.
Comparing yourself directly, for instance, to one of your favorite artists as an aspiring artist yourself can establish this contrast and help you focus on specific areas of improvement.
I'd have personally found it more useful to me to be relatively hard on myself when trying to improve, even being rather brutal on myself in some cases, but only because I've found that it has worked for me.
Obviously you don't want to try destroy your own aspirations, and I'm not suggesting you berate yourself with arbitrary criticism.
I'm suggesting you find your flaws, and focus on them intensely, while being critical of your own work.
I would let praise go to my head and is something I had to essentially compartmentalize as a product of my own progress rather than an indication of advanced skill.
You'll much better recognize the lessening of the contrast in quality of your abilities and where you want to take those abilities than your peers.
That's not to say you should ignore praise however, exterior confirmation that progress is being made can be very re-assuring or motivating, as progress is everything.
Practice ritually, with focus.
Progress is extremely important and is a product on consistent practice.
Like going to the gym, forcing yourself to set a specific time of each day to practice will make it much easier to focus and make consistent progress as you eventually won't be withdrawing time and energy from your day as you must initially.
It can be argued that working in 90 minute intervals, followed by a break or perhaps working as long as possible to upwards of 8 or more hours may be better depending on the person or the skills they are trying to master.
Either way ritualizing your practice is monumental.
There is no quick fix.
Like buying some contraption whose advertisements claim to "target and eliminate belly fat" or a book promising to promote you to fluency in Yiddish in a month, it is common when looking for information on developing skills to be offered quick and/or easy solutions with minimal effort required on your part.
So much content is now focused on brevity that it is extremely easy to be veered away from an effective developmental path.
More people will simply look for easy solutions so it makes sense that content creators will try to provide that.
If your looking to be great at something but want the process to essentially be automated, easy, or fast, you're setting yourself up for failure.
To be good at something, it takes time, and to use that time most effectively you must ground yourself and practice practice practice.
Don't be too easy on yourself, ignore things that distract you and hinder your progress, you owe it to yourself.