What tackle to use
10 - 14wt outfits, reels with good strong drags, lots of backing. Gloves are a good idea for both the fight and landing the fish
What flies to use
Poppers; Crease fly; Gurglers; Deceiver; Thing; Clouser.
Big noisy surface flies are the go for savage visual hits - but also any big fly fished anywhere near them will work when they're hungry. Think 4/0 and upwards with the general rule being the more noise you make, the bigger the fish that will hit your fly.
Once hooked a large GT will rush for cover of any nearby structure - big ones almost always make it home so crank down the drag and hold on. They have a hard mouth so big sharp hooks should be set hard. Small and medium sized fish often travel in pods but larger fish are travel alone or in pairs. The tail scutes are very sharp - wear a glove or just don't grab it by the tail.
Sight casting to large fish in shallow water is an awesome way of targeting these fish.
Otherwise get a mate to throw hookless poppers around likely holding spots or reef and throw flies at the fish that chase the popper in.