First off, use an epoxy based resin for your fiberglass work.
The polyester resins will attack the foam.

Precut your fiberglass to lay nicely on the hull, then set it aside.
Coat the hull with your resin, then press and brush the fiberglass back onto hull.
Wear gloves, and use your hands to hold one area of fiberglass in place while you brush,
or use your other hand to press the fiberglass into the resin and against your foam hull.
This will help keep the fiberglass from pulling and bunching into wrinkles.

[8D]