When cast into water, the insect imitation must appear to the fish as though it is not connected to the line. Fish that eat each other are usually more aggressive and less selective than bug-eaters, but can be confoundingly difficult to catch. Start out by investigating the environment. Memorize maps, and when you get to the real place, begin filling in the details. Don't confuse cover and structure like so many anglers do.
Structure is the shape and contour of the bottom.
Cover refers to things like specific aquatic vegetation or sunken trees. Break the habitat into categories, try to find patterns consisting of common cover options and structural elements. Get a picture in your mind's eye of all the options. If the species is new to you, gain insight into the forage options and seasonal habits of what you're trying to catch. Look at its shape and size.