Think like a fish
What I mean is; pretend you're a fish when you look at the water. Think about where your fishy self would swim and hold. It might be in that calm spot, behind that weed patch, over that dark bottom or under that rocky overhang. Fish generally like transitions: calm and current, light and dark, warm and cold, clear and muddy. Cast your fly where you think a fish would feel good.
Fishing based on a more or less qualified guess is better than fishing randomly and unintelligent over any coincidental spot on the water.