Kids Learn to Write

What are some effective ways to teach a preschooler to learn how to write letters and numbers?
The apps will puts a bunch of colors dots down in the shape of the letter, and the kids trace the dots, when trace the dot, it will have stars explosive, it’s more interesting for kids to learn!
Before children can start to write letters, they need to learn to recognize them and understand that each letter has its own sound ?
Yes, each numbers and letters will have three phonics, English, Mandarin and Cantonese.