I'd say that the first step is to work on composition/subjects.
Professional have better materiel and skills, and there is also a lot of work editing the pictures, but if your subject is not interesting and your composition is boring the pictures will be bad no matter what.
Look at pictures or paintings* that you like and try to understand how the different objects are placed - the strength lines they form, where they are in the picture...
When you take a photo of a foreground subject (like a person, an animal), try to have a nice background (and to wait patiently until any unwanted tourist has left the field !). Don't put your subject in the center, but try to put it at one third on the left or the right - unless you want to emphasis symmetries or stability. Have horizontal lines to give a feeling of stability, vertical/diagonal lines to give dynamism, and put your subject at the intersection of your main lines to direct the eye to it.
Also an easy improvement is light : forget about pictures inside, they are almost always bad. Don't use a flash, artificial light is hard to use well. The sun is your best friend, but you should always try to have it in your back when you take a picture - that way the subject is well lighted and you avoid being against the light. Sunset light makes any crappy photo looks good.
Similarly, great color contrast helps a lot, but it is very hard to take a good picture when the subject and the background have similar colors.
*I'm not that much into still-life but I think they are great to look at compositions.
Look at their photos. If you like them, they know their subject (though perhaps not how to teach it). If you don't like them, find a new instructor. Rinse and repeat. Most tutorial people put their photos online to some extent, so this shouldn't be hard -- and unlike many domains (e.g. woodworking) -- looking at the photo on your screen should be enough to judge it pretty well.
If you can't tell if you like them, I suspect that your first step should be to try to develop your "taste". Start by just looking at tons of pictures. I recommend one of the photo-apps that isn't instagram, though instagram can work. Flickr used to serve this role. For a while I think 500px did. Not sure where to go now -- but I would try those at first. Look at pictures. Rate them in your head -- based on your opinion. Once you're confident looking at a photo and judging it -- start trying to figure out what about them you like and dislike. "Thats too high contrast" or "I love the black and white", or "I love the aerial perspectives". Then go and try to change the pictures you take in that manner and/or return to YouTube to find someone who's pictures are like that.