A lot of people use #18 black w/ red wire gold head or #18 black w/ silver wire silver head. I like to fish them 1.5' - 4' below a dry fly. Use something you can see like a #14 or 16 parachute. Any fly that you can see well will work. I like the faster water around shoals but a lot of guys fish the slower water. There was a post a few days ago by troutslayer3393 where he was fishing slower water and caught some nice fish. If you use yarn as your indicator i would use the smallest piece i could, but thats just me, i don't like using a tennis ball for an indicator.
LIVE WORK AND FISH LIKE THERE'S NO TOMORROW