Here's a technique I worked out recently for adding leaf litter to an area. All of the textures used here came from CG Textures. I'm on Photoshop CS6, but I think all of this will work in CS5.
Suppose you have a nice little outdoor area, like this random pedestal in a field:
As you can see, it's got some mud and grass layers, basically the same as in madcowchef's tutorial. I made the stone pedestal in a separate file, also using madcowchef's techniques, and pasted it in as a layer by itself.
Now we want to add leaf litter. Because dead leaves can be blown by the wind over everything here, the leaf layer needs to be above the pedestal. Here it is, using a dead-leaves texture from CG Textures:
Of course, it obscures everything below it. To fix that, change the blending mode of the leaf layer to "Lighter color". Like this:
This makes Photoshop compare the colors of each pixel in the leaf layer with the one directly beneath it. If the leaf color is lighter, then it's visible. If the leaf color is darker, then it vanishes. The end result is that only the brightest leaves are actually visible.
If that's all you need, you could stop there. But if you want a little more control over where the leaves go, hide the leaf layer with a layer mask, then selectively reveal the spots where you want leaves.
You could just use a round brush for this, but that tends to make it look odd. Here's an example:
If the brush is soft, the edges of the leaves blur into the grass too much. If it's hard, you wind up with leaves cut off. And either way, you tend to wind up with circles of leaves.
To correct that, let's use some brush dynamics. I use two things. First, in the brush palette, turn on Shape Dynamics. Here's a screenshot.
The minimum roundness has been set to 31%, and the roundness jitter turned all the way up to 100%. That should help avoid overly-obvious circular curves.
Second, let's turn on scattering:
That has some pretty aggressive scattering -- 248% on both axes, a count of 2, and a count jitter of 86% (making it likely that you'll get more than one ovoid often through a swipe).
Now we can scatter leaves across the area. Thus:
Due to prevailing winds, the leaves have fetched up on the left side of the pedestal with a clear area to the right. There are a few spots where the leaves don't look right -- either partially cut off, or overlapping something they shouldn't, such as the edge of a stair. I'll fix those up with a standard brush.
You can go as far as adding or removing individual leaves, if you like. If the pattern becomes too obvious, you can also add a second leaf layer rotated widdershins, as with madcowchef's grass.
Hope this is useful to someone.