My view of preschool is pretty simple. As in, keep it simple. Overall I think the transition into school should be a natural and slow progression through stages.
For our family the first stage is like this 'manifesto' that I wrote about a while ago.
Play, laugh, explore, love, and be free.
The second stage is much like the first, with an bit more emphasis on rhythm, or 'structure'. This means that our preschooler will be encouraged (totally optional) to join us every school morning for circle time filled with seasonal songs and stories. After circle time I like to offer a variety of hands on projects for my child to engage in. And usually he chooses his own thing. And that's perfect.