The first cast made on a small stream will usually be the most productive - if you choose your spot carefully.

Trout want two main things in life; food and shelter.

Getting them both in the same place is ideal. In the photos below I mark shelter-only or food-only spots in yellow. The red (hot spots) have both.

Piru Creek at Concrete Falls is a great example.  Where the falls come in, the oxygenation is excellent and it's full of food, but to take full advantage shelter must be sacrificed.  This is what is indicated by the yellow mark in the middle of the photo.  The other yellow marker is primarily a shelter spot.  It has structure that will give relief from the current and many nooks for hiding.

The hot spot has both of these.  An over-hanging structure and within close proximity to the food source.  This is where I would (and do) cast first.

 Under-cut rocks are excellent shelter.  Dries or nymphs worked close to the rock should be productive.

 In this small creek there is a food lane running down the center, and trout laying there can be counted on to be aggresive for dries or nymphs, but unless it's early in the morning or late evening, it's doubtful that anything caught on the yellow marker will have much size.

The hot spot here, is just off to the side where there is an undercut bank and easy access to the food.  An quiet upstream approach will probably have success here.

 Same creek, and same comments as the slide above.

This spillway is an awesome spot for Browns.  The foam-line carries in plenty of food and the trout are quick to strike.  As Ed Engle once said at a seminar I attended, "Where there's foam, there's fish." The only thing I like better than a foam-line are the sheltering areas off to either side.  These hot spots still get plenty of food that gets trapped in the foam, and has the advantage of not being exposed in the middle of the creek.  I would ignore the foam first... it's not going anywhere, and take a shot at a lunker laying up under the bank nearby.

 This last shot is an excellent shot of good shelter, that was holding fish when I threw in.  The current was slow and the trout were grabbing spiders and other bugs dropping off the tree roots.  I had good luck casting against the tree and letting the fly bounce off and land in the water.  Of course I lost flies, but it was a blast, because those fish were looking up and took the fly without a moments thought.

 I hope this helps you out.  The thing I hope you take away from it is that the first cast should be at the honey spot.  Usually the bigger, more aggressive fish claim the best lay.