Are there insects on the water? In the air? Crawling in the streamside vegetation?
How is the water clarity?
Is the water higher or lower than normal?
Can you identify likely holding spots—behind current breaks, near structure, below riffles, etc.?
Do you need to get in the water, or can you fish from shore?
Is there a good place to get in the water that will avoid spooking fish and position you well to cast to likely fish-holding spots?
Are there any wading hazards you’ll need to avoid?
Are there any obstacles that you’ll need to avoid while fighting a fish?
One way to train yourself to look first is to avoid putting on a fly at the car. If you have to stop to right at the water’s edge, you can also use that time to observe, assess, and plan your attack.