It's about an hour drive. You'll need a $5 NW forest pass to enter the monument. You can buy one at a coupe places around town or the booth on the way up to the caldera. The booth is only manned till about 5 p.m. so if you show up later don't worry, nobody will care if you don't have a pass.
For flies, the most common bugs on the lake are callibaetis, midges, damsels, and a few black caddis near the bank. For dries I stick mainly with a tan parachute or comparadun in about size 14 for the mayflies or a black midge dry in about size 20. For nymph I usually stick with something like hares ears or pheasant tails in about size 14. Lots of guys fish streamers during low light for the big browns, but I seldom do, preferring to fish dries. Guys I know use black, brown, or olive buggers, or sometimes brown and gold streamers to match the tui chubs that live in the lake. The beach between the resort and cinder hill campground is a great place to wade and fish, don't let all the people and watercraft scare you, the fish don't seem to notice them. The beach has a lot of sharp pieces of obsidian, so don't go barefoot, and if a rock floats by it's just pumice.