When shading, try to keep in mind that shadows, most of the time, are not black. Using a darker shade of the color you want to put a shadow on will make the transition look much smoother.
Also, you can try using the complementary color of the base one to apply shadows.
It's OK to draw the same things over & over again. You don't need to stop doing that. If you've found your comfort zone, it's fine to not leave it, as long as you're happy there. Many artists are well known for having done that, painting only portraits or landscapes.
In 8 or even 9 out of 10 cases, your finished artwork will look at least acceptable, despite your raw line art/sketch hasn't been "love at first sight". Don't throw that thing away, just give it a chance & see what becomes of it. You might be in for a pleasant surprise.
Art isn't about being perfect, it's about expressing yourself. You aren't a robot or a camera, so don't be afraid of "messing up". You will make mistakes & get frustrated, but that's normal - even for professionals. As long as you're enjoying to create art, just do it.
The quality of your art supplies is not as important as your drawing skill. An artist who knows what they are doing would be able to create a stunning artwork even with a ballpoint pen drawing on a paper towel. Improve your skills first, then get better supplies.
Fea Crow