Although this is a rather complex question and will vary depending on the geographical location, time of year and even moon phase (all of which are often near impossible to combine to an actual workable date and time for most people), An hour before and after both high tide and low tide are generally considered primary fishing periods. Furthermore, you will usually also find great fishing shortly after the sunrise and the sunset.
Falling tide: A falling tide occurs when a tide changes from high tide to low tide and is the best time of the day to fish. Generally the best time to take advantage of a falling tide is two hours before actual low tide.
Rising tide: A rising tide occurs when the tide is changing from low to high tide. Although it is generally considered slightly less favorable to fish in a rising tide as compared to fishing in a falling tide, thanks to the movement of the water and the feeding activity of the game fish fishing is almost always still substantially better than at many other times. As with a falling tide, try to time your rising tide fishing about two hours before full high tide to make the most of fishing in a rising tide.