Here are some hints for the novice fly fisher to help make their dry fly fishing more successful. One thing many anglers do is rush right into the stream upon arriving at it. You should always stop for a moment and note what is going and then make you decision as to what fly you're going to fish with.
Always fish the correct combination of leader and tippet for the size of fly you're using. Use the divide by 4 rule if it is rough water or the trout aren't too shy, size 12 fly divided by 4 = 3X tippet. If the water is smooth and the trout are shy use the divide by 3 rule, size 12 fly divided by 3 = 4x tippet.
Use a floatant to help keep the fly you're using riding high and dry, but only use the silicone types like Gink or Aquel on a totally dry fly, once the fly is wet or slimed by a fish use a desiccant powder type like RioTop Ride which will dry and add a floatant to your fly.
Basic tools and fly fishing accessories
When fishing to a rising fish, if possible get into the best position for both casting and getting a good float, this may be downstream, upstream or across stream, or any combination of these positions. Get as close as possible without scaring the trout before making your cast.
Make the first cast count, very often a feeding trout will take a properly presented fly on the first drift over its' head, your odds go down with every cast made with the same fly.
If the fish aren't taking your fly and you're confident in your choice of fly go with one size smaller, often this will make the difference.