There isn't too much you can do with preschoolers. Their attention span just can't take it. Its the rare student that will sit there for any length of time to do pages of work. So you need to get creative with teaching them their numbers and letters. You can do flash cards. There is any number of books for preschoolers you can buy or you can print off pages for free on line. But where is the fun in that? You want to set the right tone early on for school, that it can be fun and rewarding. You want to teach a child to learn for themselves. But how do you do that? You do it by letting a kid be a kid. Teach them as they play. Or When they color.
My 3 yr old was coloring me a rock monster, as seen here: