When using Command+Tab to switch between apps, you can quickly glance at each app’s open windows to find just what you’re looking for.
After you open the switcher with Command+Tab, keep your thumb on the Command key, but move your other finger from the Tab key and press 1. All open windows from the app currently selected in the switcher will be highlighted, while windows from all other apps will briefly be hidden. Update: the feature is called App Exposé.
Once you’re in this mode, you can actually remove your thumb from the Command key. If you hit Tab, you can cycle through windows of each app in their order of appearance in the app switcher. You can also Command+Tab again to pick a specific app. You will stay in App Exposé until you click a mouse button or use arrow keys to pick a specific window, then press Return.
Update: Hat tip to reader Joe Harris, the feature is called App Exposé, and if you’re using an Apple trackpad, you should also be able to trigger it with a three- or four-finger swipe downward. If it doesn’t work for you, go to the Apple menu > System Preferences > Trackpad > More Gestures and see if App Exposé is enabled.