Be patient

Sometimes giving that fly a few extra seconds to drift into the back end of a pool will trigger a response.
Even if the cast isn’t great, let the fly sit for a few extra seconds. The longer your fly is on or in the water, the bigger a chance you have of a fish taking it.
If a fish goes for the fly, you will usually have a second shot at it, so hit it again then move on.
Drop a nymph, and wait, twitch. Let the nymph or 2 nymphs hang an extra second or 3 or 4 at the end of a drift.
Be patient.