Try incoming and outgoing tides around high tide. Sometimes night is the best time to fish, in which you use flies that push water under the surface, or poppers. Early morning can also be productive. Other times you can get the fish in anytime of the day. Experiment with different fly colors and sizes, and go to a local bait or fly shop to see whats working. Thats probably your best bet. Also, be patient. Fish don't just see your fly, they "hear/feel" it, so it can take them some time to find it.

Good luck,
Chris