While I am not the master who makes perfect Illustrations using Brush or Pen Tool but still I am trying to made this tutorial to help the less experienced or beginners. In this tutorial I will draw this pretty girl ;-) wearing a carnival mask.

Final Image Preview:

https://lh5.googleusercontent.com/-jfFiu1XHX6M/UqljkiNQl4I/AAAAAAAAAR8/JF6u0Sk9F6c/w364-h418-no/mask5-01.jpg

For the reference you can create your own design or you can use any downloaded image. Personally I do prefer draw outline or sketch first. Just draw the outline for the base what you want.

Step 2: Lock the layer of base image or Reference image & start with a new layer using existing base image as a guide.

Step 3: Lets start with the line art. You can start with tracing the outline and then continue with the inner details. I did this using the Pen tool (P). (I n case of using brush tool you should go to Object Path > Clean Up, to fix the empty paths that may cause you unnecessary problems

Step 4: When you finish your line art select the object with Selection Tool (V) and start adding color using the Paint Bucket tool (K) or Gradient Tool (G).

Step 5: After you add the proper fill colors dont forget to press the Expand button. (Expanding objects may be helpful when you want to use an object that is native to Illustrator , such as a mesh object in a different application that doesnt recognize the object.) Step 6: Weve finished adding colors but it looks like we dont have enough depth as with most vector designs.

Step 7: In order to give a sense of more depth, we need to add the shadows and lighter areas to the Illustration. So you need to select the desired shape with the Direct Selection Tool (A). Draw a filled path with your color around each area that has the same color.

Feel free to experiment. This is how my Carnival Girl looks at the end