RE: Pre-season
As the others have said, do not call them at all during preseason. I've stopped doing locator calls during the season because of all the other hunters. Everybody thinks you've got to hoot a few times when entering the woods!!!
Getting out an hour before sunrise and hearing the forest wake up is a great way to pattern the turkeys in your area. They will gobble on their own at first light. You might even be lucky and close enough to hear their tree yelps, fly down cackle, and maybe a boss hen yelp.
Going out an hour before dark is a great time too. You'll be able to hear boss hens yelping to get everybody organized, the wing beats and branches snapping when they fly up, and maybe a tom gobble once he gets situated in his roost.