At some point I too tried to do this, but the Android Studio doesn’t work quite like Eclipse does.
It's simpler: if you create a project at, say /home/USER/Projects/AndroidStudio/MyApplication from there on all new projects will default to /home/USER/Projects/AndroidStudio.
You can also edit ~/.AndroidStudioPreview/config/options/ide.general.xml (in linux) and change the line that reads <option name="lastProjectLocation" value="$USER_HOME$/AndroidStudioProjects" /> to <option name="lastProjectLocation" value="$USER_HOME$/Projects/AndroidStudio" />, but be aware that as soon as you create a project anywhere else this will change to that place and all new projects will default to it.
Hope this helps, but the truth is there really isn't much more to it other than what I explained here.
Let me know if you need anything else.