Long time since I fished Ascension Bay - too long! But we were there in July.
I would recommend long pants when wading. There's some sort of water-flea that can play hell with your thighs and any other exposed parts
- not serious but not pleasnat either.
When the sun goes down the bugs come out in force so take plenty of deet.
Out on the flats be ready for permit at any time. You might see schools of smaller sickle tails on the flats or some serious bruiisers cruising along the edges. If you have the guide to yourself and have a spare rod you can be ready and rigged for any eventuality. Take crab flies!
Otherwise the usual gotchas and shrimp variants in 6s and 4s should see you well.
Not sure what the status of the guides is these days. When we were there about 10 years ago, they knew where the fish were but didn't know much about flyfishing which suited us fine. Things have probably changed a lot since then.
Out front in the surf you might have a shot at Tarpon. They run the beaches in July and August.