I'm proud of what I do, and am most days able to recognise that hey, I'm pretty good at this stuff! without it feeling like I'm bragging or being arrogant. I do, however, realise I still have tons to learn, and definitely have weak spots in my art skills. The same goes for writing skills.
As for improvement.... I wish I had more time to do it, but I practise! I set myself challenges, and try to complete them. I do lifedrawing when I can, and use reference photos for complicated stuff. I try to analyze images, pick them apart and figure out why they work - or why they won't.
Of course, doing a long form comic also means I have to figure this stuff out on a regular basis. I set this chapter in a bamboo forest - time to figure out how bamboo forests look! And this chapter is set in a city full of festival crowds - better sort out how to draw crowd-scenes!
It's the same with writing. I read a lot. I reads tons of comics, tons of books, articles, heck, even poetry - and I try to figure out why the stuff I enjoy works, and why the stuff I don't enjoy falls flat. Once I've figured out what makes other people's stories tick, I try to apply that to my own work. And practise a lot. Writing an ongoing long form comic teaches me one set of skills, while writing a shorter oneshot teaches me another, and so on.