Get a quality pair of polarized sunglasses. The right sunglasses are essential when trying to spot fish. Sun on the water causes a lot of glare, making it quite hard to spot fish. Polarized glasses removes that glare.
Fish midday. Fishing early and late when fish are more actively feeding increases your odds of catching them. However, for learning to spot fish - and thus better understanding their movements, preferred lies and feeding habits - the middle part of the day when the sun is high overhead gives you a better advantage. A high midday sun means there is little glare on the water, allowing you to more easily see into the river.
Approach the stream carefully. How you approach a stream is critical to your success. Always walk gently, never stomping your feet. Keep low, even squatting or crawling if the fish are spooky. Stay in the shade if possible. If you wade, go very slowly, keeping your ripples small and close to your feet.
Look for a fish's shadow on the streambed. Even the most experienced angler has difficulty spotting the actual fish holding in its lie - just ask any osprey. Millions of years of evolution have given trout an amazing ability to blend in with their watery surroundings, but there is a trick you can use: look for the fish's shadow.