Have you ever been frustrated by the amount of materials available when you are creating a family in Revit?
If you start a new blank family in Revit (I start with Generic Model family templates first), the materials dialog box is almost empty.
Now you can easily duplicate existing materials in this dialog box and assign different Render Appearances, but if you want to save some time, you can use Transfer Project Standards to transfer additional materials from another proejct, family, or template.
Just make sure to have the other file open and then go to the File pull down menu and choose Transfer Project Standards. A dialog (below) will appear that lets you select the items you want to copy in. You will not be able to transfer everything you can transfer from a project to a project, but you can get materials.
Once this is done the materials dialog in the family will be loaded with all the materials from the project.
A important thing to note with doing this though is that you will add to the file size of your family and decrease its performance in Revit. I would recommend deleting any Materials that you do not need from the dialog after doing this.