Look for a good reference, from books, magazines, art, or the Internet, which resembles a great character whom you want to draw.
Let this reference have good similarities to your drawing; like the pose of the character, or the fashion of the character, of the facial features of the character.
Then mimic these examples into your drawing while experimenting with how you could change some elements in order to be original.
I am into drawing comics, or manga (Japanese styled comics), and if you want to know more, visit my hub or http://manga-journey.com/.
If it's other genres of art you talking about, the above is a good guideline for you to follow.