In this video-tutorial I show some basic extrude actions for faces with blender:
One method to scale a selected face down I use in this video is inset faces. It is very helpful when you want to extrude a face for which you wish to reduce the size before. Another method to do this is to extrude the selected face, cancel the extrusion with escape-key immediately and then size the selection (which is actually the copied face cause you canceled the extrusion before). The drawback is that you have to remove duplicate vertices which you don’t have to do when you use the inset faces method instead.
What I also demonstrate is constraining the extrude to a certain axis, in this example the z-axis. When you press E-key to extrude a face for which the normals point to the z-axis, then the constraint is automatically choosen for the z-axis. You can remove this constraint by pressing Z-key. Pressing Z-key again will reactivate the z-axis constraint (same for x- and y-axis and -keys).