Alright, most of the stuff I was going to say has already been said, make use of layers, learn about things such as clipping and smoothing, watch tutorials, don't abuse the airbrush, shade properly, etc, etc, so I'll try not to repeat stuff too much.
With art software, I'd recommend starting with something free.
Medibang/Firealpaca is a great program to start with but can be quite limiting. I personally dislike it but my overly talented friend swears by it so I guess that's just a preference thing
Autodesk Sketchbook is another great one for beginners, it's very well-featured, easy to figure out, the brush customization is fabulous, it has some more traditional-style brushes/features which makes transitioning from traditional to digital art much easier, and the only thing it really limits is the number of times you can undo. (it also doesn't have clipping yet, unfortunately…)
Krita is absolutely incredible, the closest thing you'll find to free Photoshop. It's by far my favorite out of all of them, however, it can be quite difficult to start with because there's just so many features that you can easily get lost in it all. Still a 10/10 program tho
(There are a ton of other great ones out there that I didn't list, so if you have questions about any software just let me know.)
For tutorials, I always recommend the same exact stuff but that's because it's really great advice
-https://www.youtube.com/watch?v=02xAH3HlcEM&list=PLLmXZMqb_9sbNLM83NrM005vRQHw1yTKn
^The 10 minutes to better painting series, which, despite the title, applies to so much more than just painting
-https://www.youtube.com/watch?v=FPz8Xyt3z-w
-https://www.youtube.com/watch?v=FPz8Xyt3z-w
-https://www.youtube.com/watch?v=7fLV5ezO64w
-https://www.youtube.com/watch?v=gwLQ0cDb4cE
^More stuff that might help you or might not, it's just good stuff to know
-https://www.youtube.com/watch?v=OEv6MdbjwZw&list=PLhG73R7q9Bl8D3Pa4Z6qcajA3zIilbo1V
^A bunch of anime tutorials, I've only watched like three but they're good
-https://www.youtube.com/watch?v=gQIxdrNrG30
^Common digital art mistakes
-https://www.youtube.com/watch?v=yP0KG3-nIzk
^Digital art hacks
-https://www.youtube.com/watch?v=mIZwUsAnRtg
^Weird stuff that makes your art look more professional
-https://www.youtube.com/watch?v=IVbqoy_JEV0&list=PLflflDShjUKH4EfZyf0vuKEuqeqvlV0Qd
^The anatomy quick tips playlist, which I realize isn't what you came here for tutorial-wise but I recommend it to everyone anyway because it's the greatest thing ever
-https://www.youtube.com/watch?v=D6tmUJAv_k8&list=PL3BE843C2DE5DC6AC
^A bunch of random things, some more useful than others
-https://www.youtube.com/watch?v=k0ufz75UvHs
^Once again, not exactly what you may have come here for, but here's a nice tutorial that helps with general art improvement
Really any tutorials by Sinix Design, Marco Bucci, Sycra, Pluvias, Ross Draws, Sara Tepes, or WLOP are guaranteed to be good.
…I can't think of what else to say at the moment but yeah, there's some stuff
hope it helps