1. Always try new things
Explore new concepts, different angles and perspectives. Even styles.
2. Draw broadly
Never start your art with details. Get the basic shape down solidly first, and then add details to it.
3. Stay focused
If you're not thinking, you're not drawing. Never have your mind wander off mid-drawing.
4. Have an idea
Know what you try to paint, right down to the final image. Come up with an image in your head first and draw based on it.
5. Feel the dimension
For every objects and characters you draw, try to have a good feel for how it is shaped.
6. Always study
Where ever you go, try to analyze and process what you see in your head. Be it subway train, or crowded park. Look for particular cues, highlights and shapes. Use that knowledge to improve your art.
7. Try to enjoy it
If you're having fun with the piece you're drawing, you'll be more involved and motivated. Even if it means drawing naked chicks all the time.
8. Take as long as you need
Your art is never done until it is.
9. Trust your eyes
Your eyes are always correct even if your brain wants to deny it. Don't trust what your brain says - if it looks funny, it probably is.
10.You already have everything
You have all the tools and talent you'll ever need. The only thing you need to change to improve yourself is to change the way you think.
11. There's no such thing as a bad style
Just bad art.
12. Never copy
Never copy other works to produce your own work. If you really like something, try to study how the artist was able to create the effect and attempt to replicate it from your head.
13. Keep your strokes economical
Making multiple strokes to create an effect isn't always the best way. Sometimes it can be done in one stroke or two, and it'll look better that way too.
14. Get your sketch ready
Make sure your sketch looks good before you color it. No amount of paints will save a crappy sketch.
15. It'll take a long time.
Be patient. Be it your current drawing, or your career, art is something you do for your life. Patience is indeed a virtue. Keep a calm and steady pace and you'll be fine.
There could be few more, but so far this is all I can think of. Maybe there is a lesson of value to you here, or maybe not. I hope this will be helpful to someone out there.