1. Get a sketchbook and draw something once a day for two weeks.
Why? Because practice makes perfect, and in two weeks, even if you don't notice it, you will have improved. Draw what you see. Draw what you imagine. Draw what people ask you to, or don't. Make sloppy, nasty sketches or elaborate masterpieces. It doesn't matter. Just DRAW; the more the better.
2. Look at one of your favorite artist's techniques and try their style.
NO copying! Create an entirely new piece but do it in their style. Why? Because your style will mesh with theirs, and you may learn something from the other artist's technique that you like and can use to build upon your own.
3. Think of the style of art that you dislike the most and make yourself try it.
Common sense: most artists don't do styles they don't like. But try it anyway. Don't like abstract? Try it. Don't like comics? Try it. Even if you hate it the whole time you're doing it, doing something so opposite of what you usually do could open doors of creativity, inspiration, and realization.
4. What do you specialize in drawing? Well, draw something ELSE.
Everyone has a preference of subjects. Many artists specialize and limit themselves to drawing what they love. This isn't a bad thing. Do what you love. BUT try to draw something out of your norm once in a while. Draw mostly people? Draw something from the animal kingdom, a cityscape, or a still life of some apples. Well-round yourself in all areas and drawing what you love could improve by volumes.
5. Try a new medium.
Again: Do what you love. But again, trying new things is always a good idea. Do only oils? Try colored pencils or marker. Only watercolor? Try acrylic, graphite, oil pastels or even finger paint. Whenever you do anything new, you give yourself opportunities to blossom with new ideas, talent and inspiration. Also, you might find a medium that's your new calling and new found love! You don't know until you try.
6. Look up color schemes and try one, some, or all of them!
Black and white.
Monochrome: Multiple shades of one tone.
Complementary Colors: Colors opposite on the color wheel. (Red/Green for example.)
There are others as well. Look some up and make new art with a scheme you usually don't do!
7. Have someone pick 3 - 5 random colors and use only those colors.
In number 6, mentioning color schemes, those schemes all have a certain harmony to them. BUT, if someone picks random colors for you, you have to create harmony yourself or just create complete color chaos in a pleasing way. It will be new, fun, interesting, and maybe even frustrating, but you will have taught yourself to meet new challenges.
8. Kick your own ass.
This is a popular one on Deviantart. Take an old work of yours and recreate it. You can use new techniques or not. The bottom line is you can see how much you've grown, what you've improve on and what areas you HAVEN'T improved in.
9. Take a pen and do what you can with it.
Ink pens are the best, but really any pen will do. Look up pen work and you will see some very cool techniques with pen shading and sketching! Look at a still life and draw it, using thick lines some places and thin lines in others. Use dots, thatching and squiggly lines for shading and texture. See what you come up with, and any new creativity can transfer to your usual mediums.
10. This may be the hardest challenge: Take your best piece, hand it to an honest friend or family member, and have them tell you EVERYTHING that's wrong with it.
Try to swallow that pride! Knowing your strong points and building on them is good, but knowing where your weak points is JUST as important. Looking at your work through a different set of eyes can be very enlightening. Don't do this if you're easily discouraged.
11. Take something out of a color book.
Color in the lines like a pro. Use any medium you like and you make that flat 2d black and white picture look like a three-dimensional pixar character! Or make it some crazy weird abstract monster. OR don't even color it. Just REDRAW its simple/boring lines and do a more detailed and elaborate version of it.
12. Take what you normally draw and draw its structure.
Draw people? Strip the skin and draw skeletons and muscles in poses instead. Draw buildings? No more windows and concrete. Draw the basic layout of the interior building; what it looks like BEFORE workers put in the floors and ceilings. Why? Knowing the core of your favorite subject will help you better understand the surface of your subject as well.
13. Find all your left over scraps / useless knickknacks and create something.
Find anything from paper shavings off of scrapbook paper, to cuts of fabric, to paperclips, to discarded pen caps. Gather all those little nuisance things you'd normally throw away and instead combine it all to make art. It can be two dimensional or sculpture. You may need tape or glue. It may come out beautiful or hideous. The point is, you are TRYING SOMETHING NEW. I keep stressing this. New is inspiring, always.
14. Put your regular brushes aside.
Digital and traditional painters, try a project without using ANY of your regulars. If you've used all tools, then pick ones that you haven't mastered. Try other utensils of creation, like sponges, make-up appliers, quetips, and etcetera. Do NOT relapse back into your favorites, otherwise the project fails. The point is to broaden your horizons and potentially open your eyes to some wonderful method or tool that you were previously unaware of.
15. I will say this one last time. Trying new things can be inspirational. It promotes creativity. It can teach you new things and new techniques. It can make you come to some grand epiphany about your work. Trying anything different introduces you to other concepts. You might learn something or find something you didn't know you loved.
So here it is: Try new things and draw, draw, draw all the time. ;D
Here are some other fun challenges to try!
Make a masterpiece with crayons.
Fingerpaint a masterpiece - fingers only!
Sit in front of a mirror and do your own portrait.
Take a request from a friend and draw something for them.
Close your eyes, spin around, sit where you are and draw exactly what's in front of you.
Look up new tool-methods and try them! (Example: palette knife or sponge.)
Set up some fruit, a lamp, a blanket, and do your own still-life.
Make a picture using dots only. (dots can vary in color or thickness.)
Draw cartoon / anime versions of your friends.
OR draw realistic versions of cartoons you love.
Design a new book or movie cover to your favorite book / movie / magazine / CD.
If you have any other ideas, post them in the comments so people can see.
Have a good day everybody.