Ok so I haven't posted anything in a long time but I have been drawing, if you what to see where I put most of my drawings follow me on Twitter at Blade_Dragon
And this was a plugOk so one of the ways I got better at drawing straight lines is tracing, and no o didn't post it and said I made it. I don't post anything I traced, but you can get better by doing this, especially since I've been drawing on paper most my life and why I started drawing on my phone(and now my drawing table some time) i used tracing to get better at makeing straight lines.
All you have to do is get an image, turn down the opacity then go over it in another layer. Make sure its not on the same layer.Also you can use the trace to practice your colors and shading. I used to me terrible at coloring there would be white spots and the shading was just a darker color blurd. And when your coloring, do it on another layer Below the line art, unless you want what I use to draw.
But if your already good with online drawing this is some of my tips
1. Start with a base drawing in different colors then go over it with black
2. When you do draw a base start with the body, eyes and face, hair, clothes, then other things, and do it all in different colors
3. If your like me and can only draw humans or mainly females then draw what your good at then add what your not with it.
I'm not good with drawing males and even worse with backgrounds, so what I did is draw a girl and a boy and then the backgrounds, then my strong will to not draw trash made me go and do it good
4. I always think people can improve their art but if your over 13 you probably don't what to make any big changes to your art style, that's most of your year as a minor and thats when you get all your free time. Now I'm not saying not to do little changes, but if you where drawing cartoon characters for ten years and you what to change to full anime style, you probably won't make something your proud of, in the amount of time you what trust me.
5. Watch shows that are close to your art style or what you what to draw. Like I watch anime and sometimes I just look at how they draw somethings, and I try it later
6. Don't judge your art to others. Now you can and probably should look at others art to be inspired to do better, but don't put yourself because of it. It won't do anything, instead look at what they're doing right and how you can change what your doing while not copying them.