Children learn best through modelling. So start out by having drawing sessions with your toddler on your lap. Even better if you illustrate while telling a story. Don't worry if your elephant looks like a crocodile. You do not need to be a Michaelangelo to teach your child what a pencil can do. Later, give them a pencil and see what they do with it. If they put it in their mouth, then obviously they aren't ready. When they start making marks on paper, the answer to your question whether they are ready or not glares you in the face.
Don't rush them into drawing shapes and writing alphabets. According to Susan Striker in her book entitled "Young At Art" she says, "This point in scribbling development is so crucial to the child's normal development that it can be devastating to now rush the process or "teach" the child how to represent realistic objects." In other words, scribbling is important. Don't disrupt their learning process.
Make writing fun. Writing doesn't just have to be paper and pencil. My kids have a blast with their blackboard and chalk, and whiteboard and markers. Kindergartens these days can dish out really boring work. Kids come home copying the strokes over and over again. Where is the excitement? Check out the pictures below. Damus was happily drawing lines and circles on the animals. Karina, who is already passed prewriting stage, was also eager to do the activity.
So ignore the old lady who screams at you for giving your child a pencil that will poke his eye out. Provide the opportunities, make them fun, then sit back and enjoy watching your child grow in skills and imagination.