Agree with the write and wipe materials, used the Kumon materials (Tracing books, number/letter cards, etc.).
I started to really teach writing to my daughter at 3 y.o. She could already hold a pencil by that point. She used a large triangular art pencil, and first learned to write her numbers, Kumon-style. At 3 1/2, we started with letters, capital letters first. Every once in awhile, I’d have her trace the alphabet. I noticed that her coordination improved dramatically at 4 y.o. Now I have her trace the alphabet almost every day, and have her write words and sentences.
I’ve been using the Writing Practice Flash Kids Harcourt book, with tracing paper:
http://www.amazon.com/Writing-Practice-Harcourt-Family-Learning/dp/1411400879/ref=sr_1_1?s=books&ie=UTF8&qid=1339760374&sr=1-1&keywords=print+writing+practice+book+flash+kids
It wasn’t easy to start at 3 y.o., but she definitely enjoys writing now.
IAM REALLY Happy to see…that kids got FED UP of writing the same LETTER again n again…