Stop Preview from opening every file in its own page
You didn't say what version of OS X you're using and I don't know it Preview in different versions of OS X have different preferences however, in OS X 10.8 anyway, I went into Previews's Preferences (Preview > Preferences... > General) and changed what I assume is the default of Open groups of files in the same window, since I've never changed Previews's Preferences before now, to Open all files in one window, as shown in the image below.

With Open groups of files in the same window selected and when only opening one file at a time the default behavior is to open each file in its own window until it's changed to Open all files in one window.