In my opinion it is very different to draw from life than to draw from a picture. I personally can’t draw from a photo/image unless is a painting from the masters in a museum.
The problem with drawing from a photo is that the drawings will always end up stiff/without life. When you draw from a real person you can tell their mood, attitude or personality in real time, which forces you to think fast because a person will always move. So I say Life > photo
Hmmm.. How I developed the style it’s a little complicated/long, but I’ll make it kinda short.
In Art-school they teach you anatomy and how to draw from life, which helped a lot — but only on my draftsmanship, not style. What you need to understand about anatomy is that it teaches you the basics of the human form and once you learned the rules you can break them as you please.
The “style” comes out of you naturally. If you have to force something into your work is probably not doing you any good. I noticed I would draw things a certain way in my sketchbook (simpler, with fun shapes etc) but when I went to a final piece I would change it completely for w/e reason (I was trying to fit in etc). I stopped doing that and I stayed truth to my personal taste. I also surrounded myself with artistic influences of all sorts and my favorite things from each and every one of them got engraved in my brain. Some stayed to this day and some didn’t.
I think everything clicked when I realized what I wanted to do for a living. My biggest dream is to work for the animation industry. I bought every art-book I could, studied every movie etc and well, I’m still learning xD I still have soooo much to learn, I struggle so much with sooo many things, but I guess the more you practice the more it becomes second nature.
I hope this somewhat answered your question xD
Good luck! :D