I wouldn't call myself a skilled artist, but I think I can give a world to some of these.
On the subject of the program you're using, there aren't too many free options, but I've heard that medibang paint is essentially just fire alpaca with a few added features (I'm not sure if Fire Alpaca has textures and frames), and I've heard good things about Krita, though I don't think it is as lightweight as medibang.
On the subject of drawing, I'm just gonna paraphrase Jake Parker:
1) Build a foundation in: composition, light and shadow, color theory, anatomy, and perspective
2) Brute force it - drawing as much as you can will force you to improve. Obviously this isn't as easy if you aren't doing art professionally, but even when you have a few spare moments try to get it a quick sketch. Be consistent and it will add up
3) Study artists you like - pretty obvious, the more you study what you like and learn to understand what makes it good, the more you'll be able to learn those techniques and incorporate them into your own style. A copy sketchbook (or in your case, a copy file) would suit this purpose quite well.
4) Work on a personal project, like a comic. Sometimes there's no better way to grow than to jump in head first. Starting and finishing a personal project can do wonders for your learning. In particular you should remember that you will keep on growing as an artist, and so no matter how good your work gets, you will almost always look back on it with some embarrassment as you get better.
That's my two cents anyway. Even after drawing for years, this advice in particular has really helped me recently.