Tie your flies in various lengths from 1.5 inches to 12 inches. I disagree with Wild Bill somewhat in that I think, as a general rule, a 4 inch fly is a good starting point when you're not sure what to use or what size fish are around. In fact, day in and day out a 4 or 5 inch, all white fly is hard to beat. On the other hand, if I were fishing the CBBT today I'd probably start with a 7 -10" fly because I'd know there are big fish around.