How to show more depth?

The other ACPs are on the money in terms of the perspective and smart objects.   Also,  I might add, to include a little bit more to the illusion of depth, is to slightly blur the logos that are further away. 

I'm covering a couple of points with the one image here.

1)     I have made the Recycle Icon layer a Smart Object. Then double clicked to open it in a new window

I then added a layer in that window. 'Ctrl a' to select all, and stroked with red.

This gives us a permanent bounding box to fit to the perspective.  When done, we open the SO again, and turn off the red bounding box

2)     I have set up some guides as a semi arbitrary perspective.

We can see the horizon, so we know that is right. I have also placed a vertical guide in the centre of the image.  This gives us our single point Vanishing Point

I have placed a vertical guide each side of the canvas to use as a Three Point Perspective.  With no information in the image to set those two, I have just guessed, but they'll work fine.

Note: I use Lazy Nezumi Pro's Vanishing Lines preset to draw perspective. Set the pivot points to the three vanishing points, and I am good to go.

Make the SO about the right size for the nearest placement, and position at the right height, in the center of the image.

Draw some guides on a new layer from the vertical vanishing point (VP) intersecting the bottom corners of the SO bounding box

Use Free Transform (FT) perspective to fit to the guides. 

You have some choices to make, but by far the easiest is to stick with single point perspective just using the center VP.  If you are doing that, move the SO into position

Note I should have said a while back to work with a copy of the SO, but do so using New Smart Object via Copy

Draw some more guides from the centre VP to the bottom of the bounding box

And FT the SO to match the guides, but drag just using the center upper handle

Repeat for the other recycle icons

There's a trick you can do with Layer Styles, of reducing the Layer's Fill Opacity to zero, which just leaves the layer style.

To distress the outline, ctrl click the layer to load it as a selection, and add a layer mask.

The mask will exactly fit the layer at this stage, and make no difference

Three steps coming up...

Ctrl click the layer again to load the selection.

Go Select > Invert selection

Then Select > Modify > Expand I used 3 pixels

The selection will now intrude slightly into the layer mask.

With the mask selected, fill with black (Alt backspace)

With the mask selected use Filter > Gallery and distress the edge.  With such a small image this was tricky, but I used Distort > Glass withg values of 1, 1 to get this

It depends on the pixel size of your image as to how well this will work  — it won't work on the smaller icons for sure — but there other ways to distress the mask outline like stroking it it with a rough brush.  I'll post this as it is kind of long, and then show you how to do that.

As for the perspective, the sides of the bounding box should project to a single point on the horizon, like this:

The "longitudinal" perspective is a bit more tricky. I just did it by eye here, but maybe there's a trick for that too.

There was an excellent and very informative thread just about perspective only a few weeks ago. Can't find it now, anyone have a link?

Any advice on any of these issues

Smart Objects, Smart Objects, Smart Objects.