It's really up to you, depending on your useage, but...

For things like attaching firewalls and reinforcing gear plates, etc., I chop up the glass into pieces about 1/8th inch wide, and 1/4 inch long. It's a great use for all those scraps of glass you have laying around after a project, and really increases the strength of those joints, especially if you're securing something to a fiberglass fuselage.