The core of what to do has been pretty much said, but I'm going to throw some stuff that hopefully helps.
Probably a big chunk of becoming an artist is to visualize objects in how they're constructed. In translating objects to paper (or any 2d medium), you must convert what your eyes already see in real life to a medium that doesn't have depth.
So how do you portray depth with a flat object? You should use constructive drawing to understand that object, drawing through to understand how light affects it (since through shading, light is how we see everything) as well as it's limitations, like with joints and how they can move in some ways, and can't in others. "Construction" means you build up your object in easy-to-understand simple geometric shapes. Understanding large complex volumes with simple shapes is a step in the right direction. Having a handle for perspective, especially with these fundamental shapes (cube, sphere, cylinders, etc) will give you a much larger understanding of what I'm talking about, but it's not required.
A lot of "how-to-draw" books (especially how to draw manga) are total rubbish. Instead of being limited to drawing a very specific object in steps, you cannot necessarily understand that thing's volume, so you couldn't draw it in other angles or situations very easily. You should always practice something and understand how it can be built, than letting someone build it for you.
People say that practice makes perfect. And of course, they're absolutely correct. Practice isn't necessarily just getting into routine, it's also building visual knowledge and skill. You train both muscle memory (like drawing lines, circles, how to hold a pencil) and cementing your visual library. Drawing repetitively is essentially making "guesses" as to an optimal and correct way of drawing.
So you wake up one day, and draw a pot. It's possible it might be good, maybe even good enough with some shading and polishing to hang on the fridge! The issue is when your mind interprets it as "good". Since I'm guessing you aren't drawing pots very often, you'll fall into comfort with saying "this is good enough".
This is not a good mindset to get into.
If you draw a hundred pots, you'll start to draw it easier. (If you aren't fatigued at drawing a bunch of pots first!) Your mind and your hand know how to draw a damn pot! And once you know a pot, you'll know what makes up a pot and you can bend the rules. Make short pots, skinny pots, etc. This is essentially what getting something into your visual library is like.
People who are seriously into art will always say that you should stick strictly with drawing realism. I'm definitely not in the realm of an expert, but that isn't necessary. YES, you will most likely improve faster if you draw completely dedicated to realistic studies, but when improvements in drawing skill are in terms of months to years, you will likely be dragging yourself through inspirational mud the whole time. You want to draw manga? Go ahead. BUT, when you are wanting to improve, you should tread carefully to not get caught up in someone else's interpretation.
Drawing from someone else's creation is akin to drawing from their mind, in which you are making a copy of a copy. And like a JPEG that gets worse and worse quality as it's passed around, your interpretation is already steps away from the original "thing". Like I was saying before, it isn't a life-or-death thing to draw manga as opposed to realism, but you must be aware of the limitations of drawing an interpretation as opposed to drawing from life. (Even a realistic drawing is an artist's interpretation, it can be argued even a photo is an interpretation as it removes the feeling of depth from the real thing)
What you should do when copying from someone else's work is to understand how it is constructed. You will NOT benefit by copying wholesale from someone. At the very least, try to understand how they do what they did. Even better, you can go through sketching->lineart->coloring->post-processing to get a feel of how they get finished works.
This post will probably have some errors of judgment on my part so I might go back and edit + add some images later to split up monotony and make some of what I'm saying easier to understand.
Biggest thing to take from all this would be to take with a spoonful of salt. Question why for every step. Draw your own conclusions. Find what works for you.
