As with evergreen cones, so with evergreen branches: some types may suit your purposes better than others for designing a kissing ball.
The branches of eastern white pine trees, for example, are not only pitchy, but also soft. The branches of many other evergreens are more rigid, making them easier to insert into the styrofoam. Experiment with the evergreens, if any, in your area.
I cut my evergreen branches so that the average is about 10 inches long. Three inches of that length will be inserted in the styrofoam. Don't attempt to design an even globe shape with your evergreens: it's perfectly fine to layer them (i.e., stagger the lengths). Indeed, the shorter branches are especially helpful at the end of the designing process, when you're trying to fill in spaces to conceal patches of styrofoam still showing.
In the picture here, I show you how to prepare an evergreen branch for insertion. Notice that the tip, at one end, is bare of needles? I stripped those needles off. Why? Because the styrofoam quickly becomes jam-packed with material, as you insert more and more evergreen branches. Removing some needles mitigates this problem some. Besides, a branch thus streamlined will go in easier.
How do you strip off the needles? My method is to insert the bottom part of the evergreen branch between my pruner blades, then slide the branch back and forth at an angle perpendicular to the blades. I essentially "shave" the bottoms of the evergreen branches, using the pruner blades as "razors."
On Page 9 I offer more tips on designing kissing balls with evergreen branches....