I'll admit I'm not a huge fan of g/g unless it's a downright epic scene. Plain solo modeling I like, some b/g I like, but g/g has to really good for me to like it so take what I say with a grain of salt.
With that said I do have some suggestions:
1. Make sure you really like doing g/g and it isn't just gay for pay unless you can fake it really really reaaaalllllllly well. Going though the motions in a normal hardcore scene is bad enough. Doing it in a g/g scene is a waste of time for the viewer. It's better to just watch nothing.
2. Don't use any toys or any accessories. It's never as good as two women using their hands and mouths on each other. If there's one thing that can ruin a g/g that's really good to the point I might otherwise think is great enough to get me interested in it, that's it.
3. Even if it's g/g try to keep some passion in it and still have things like kissing, fondling, and other stuff.
4. Like it should be in all porn scenes, no gimmicks.
5. Try to actually get each other off.
