Check the Temps
As I've mentioned before, Fall trout fishing can be some of the best fishing of the year. Water begins to drop to ideal temperatures and really triggers trout feeding. I like to focus my fall fishing to locations with water temperatures between 48 and about 58 degrees farenheit. Any colder and fish seem to start to really slow down and if it's still warmer than this they will not usually be quite as active yet. These temps seem to be ideal for both river and stream fishing for most trout.
You can adjust this temperature range a bit for different species. Ideal temperature zones are probably about 5 degrees cooler for lake trout, dollies, and char, 3 degrees cooler for brook trout, and maybe a few degrees warmer for browns. Take a thermometer along and find water that fits in these zones and most likely fish will respond well. Hatches, spawning behaviors, and several other factors will still affect trout behavior but starting in the right temperature zones should put you on the right track.