You have always heard that a picture is worth a thousand words right?  What is a video worth?
For years I have complained that roofers cannot follow simple directions when they are printed on each bundle of shingles WITH PICTURES in English and Spanish.  GAF has hit the proverbial nail on the head with their online training series without the need for as many words.

For the last few years here in Houston I have been pointing out that roofers and builders have been improperly installing the metal drip edge flashing along the eaves wrong.  In almost every new roof I look at the installer places the felt underlayment then install the drip edge over it.

Drip Edge Improperly Installed Over Felt

The typical explanation from a roofer is that this prevents wind damage to the felt prior to installation of the shingles.  The problem is that this can also allow water which reaches the felt to bypass the drip edge and run to the lower edge of the roofing deck or into the soffits.

In reviewing the GAF materials online they explain how this procedure is supposed to be implemented.

GAF does have a disclaimer that says some municipalities may require the drip at the eaves to be over the felt; however, I am not aware of the jurisdiction requiring it.  It would not appear this should be necessary if the components are configured carefully and in compliance with normal wind load preparations.  This normally requires the drip edge to be fastened directly to the deck with nails that are the same metal as the decking strip (steel or aluminum) trimming the felt underlayment so 1 inch to 1-1/2 inches of drip edge is exposed.  The shingle starter strip will adhere to this drip edge, so its attachment is an important part of keeping the shingles on the roof.  Starter strip should be used along eaves and rakes. Starter strip is a specially designed purpose fabricated shingle that has strong adhesive patches placed where it will stick to the drip-edge material. Do not use regular shingles cut in half and mounted upside down for this purpose. Starter strip should extend beyond the drip edge ½ to ¾ inches.  If you must use cut shingles where wind loading is of concern it is necessary to hand seal the starter to the drip edge using measured amounts of adhesive to prevent a water seal between the drip edge and the start strip.

You can find all this information and more on the GAF web site How To Install Section.

Another good reference for this subject is the LSU Agriculture Center Web site.