One thing you might want to do is check out the following movies: Making it ... with Kristen Bjorn
The Agony of the Exstacy
Both are full length, behind the scenes documentaries showing one of the masters of current gay porn, Kristen Bjorn at work.
There's a lot of interviews there that probably won't help you, but you will see how he sets up shots, lighting techniques and other things that will no doubt help someone new to directing porn.
As for generating heat on screen, that's a tough one. You can't just throw 2 gay guys together and expect fireworks. If the guys don't click, that will be obvious in the scene. Maybe a good way to spark things up would be not to cut right to the sex? Start out with the guys fully dressed, and have then do a lot of kissing. Let them slowly undress each other... there's no need to send someone's mouth directly to the penis. Let their hands roam all over each other's bodies first. You want to sort of tease the audience, and make them really really want to see what's going to happen next. If you start out with the guys naked, and someone sucking cock, you lose that whole anticipation edge.

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