Drawing is difficult.
It's too easy to make mistakes and not notice them.
In the course of trying to re-learn how to draw, I've learned some interesting things. The biggest lesson learned in the process was that the geometry and overall composition of a drawing can easily become skewed if you don't constantly check for it in the process. A good way to do this is, if drawing on paper, to hold the drawing up to a bright lamp or daylight and look through the paper. If the drawing looks weird in some way or seems lop-sided, there's a good chance your artwork has fallen victim to skewing.
On a computer, flipping the drawing is usually as easy as "flip horizontal" in your graphics editor of choice.
Take my advice: when drawing, you want to correct any proportions or skewing issues BEFORE you start inking or coloring. Otherwise, if you want to correct your artwork, you'll have to do much more work all over again. I've run into this situation more times than I care to remember.
It's even worse if you never catch these mistakes and have to wait until you post it online and everyone else notices it for you. That is frustrating.
Furthermore, if you express frustration with your artwork's flaws, people who offer helpful critiques will often take it personally and think you're attacking them. People will be led to believe that you cannot accept criticism because you show frustration with yourself. This can compound problems in your development as an artist. Again, this is from some rather harsh personal experiences.
Something else I've noticed: A Wacom tablet, even if you do your sketches on paper, will help immensely. No scanned, inked, linework will ever have the fine resolution of something "inked" on the computer. You will most certainly acheive cleaner line work if you scan your sketches into the computer and ink them digitally. This technique is certainly not for purists; it has served me well, however.
A lot of this stuff is personal preference and observation. Your mileage may vary.