My daughter's preschool group, "Little Harvard," started off the year with a literacy lesson. We had large capital letters (2 printed on a landscape 8 1/2"x11") which they traced using play dough. I actually made edible play dough for my daughter to use (see recipe here).
First, you help your child roll small balls of play dough into long strips. Have them choose a letter, and ask them what the letter is. If they get it right say, "You're right! That's an E!" or whatever letter it is. If they get it wrong or don't answer, say "That's an E! Can you say 'E'?" Then you show them how to use the strips to trace the letter. When they are done, reinforce the letter: "Look! You made an E!" It's a lot of fun, and really simple. And you can focus on just a few letters at a time. I'm sure this would work great for numbers and shapes as well.
Note: The edible play dough is a little bit greasy (especially compared to the regular stuff), so I would recommend laminating the letters so they can be reused. These ones got a little gross and just got thrown away. Even if you are using regular play dough, you might want to laminate the letters just to make them a bit more "toddlerproof."