Lets begin with the first and foremost basic step which is creating the environment or the background for our icon. I have overlayed and added some shadows to my back ground so you can just save my background and start working straight from it.
Our first step would be creating the custom shape which will be the Diamond Card from your Custom Shape Tool's selection. So grab that shape, set the background to white, and create an average size icon to the left hand side of your background.
Now that we have our shape, lets add some base to it so that it will look more bulky. I have put together a list of Layer Styles you should apply so go to Layer > Layer Style > … and begin!
Looking good. Our base is complete so lets begin to add details that will start the finish cut of our icon. Grab the same Diamond Card Shape and create the same icon except smaller and inside the base of our icon. Oh and set the background to #ff6c00.
We are getting closer to home so now that we have the finish cut of our icon, lets put some more detail on it. Duplicate the shape you just created and apply the following Layer Style:
Results
Duplicate the same shape again and clear all layer styles. Now rasterize the shape and grab your Burn Tool. Start touching the left hand side of the orange diamond and moving to the bottom. Grab the Eraser Tool to do some minor touch up on the area's that stood out a little.
Results
Now lets add some shine to it. Duplicate the original orange diamond again, clear off any layer styles and grab you Dodge Tool. Set the size to 110 and touch up on the top side of the diamond. Grab your Eraser Tool and finish touching up on the area that stand out.
Results
We are almost in shape, a few more details and our icon is ready to be used. Duplicate the orange diamond again, set the background to white and rasterize it. Then grab your Elliptical Marquee Tool and cut off a nice chunk, you can follow my guides beneath. Once you have cut the shape, set the Blending Options to Overlay. Use your Eraser Tool to touch up on the areas that stand out.
Results
You can give your self a nice pat on the back as we have just completed the most difficult part of the tutorial. Everything else should go with an ease, so lets get to it. Go back to your Custom Shape Tool and from the list select School. Place the shape in the center of the orange diamond and go to Edit - Transform - Flip Horizontal.
Results
Lets add some detail to our newly installed shape. Go to your Layer - Layer Style and apply the following styles:
Results
You are now done, you can go ahead and duplicate the icons and resize them. After playing around a little, I got this:
More Tutorials: 
I just read you tutorial but unfortunately i already failed at the first step! I could not find the diamond custom shape you are referring to. I only have about 30 shapes. I also researched the internet about some more custom shapes, but i was unable to find a the diamond. Maybe you could specify where you got this particular custom shape from, or if you created it by your self and how?
Best Regards
Lanoxx