Sparkey said it best, "presentation." Any fly will catch a fish, but if it isn't in front of the fish, it ain't going to take it. As a rule of thumb look for water traveling at a speed of about a man's walk and less than 6 feet. Early morning or high water, try throwing your fly close into the bank and working out towards the seams..

As far as patterns go, use one that you have confidence in. Everybody has a particular pattern of choice. I like fishing big marabou patterns tied on tubes... followed by Spey/Dee's and then GP's.

Lastly, hang in there... Winter can be especially tough with a fly.

Downriggin'