For setting directory in file open/save dialog, you have 3 options, which are presented via Settings -> Preferences -> New document/Default directory tab, and changed on the fly:
- Directory will be set as the current document directory.
- Directory will be set as the last operation directory (ie. where the last time you save or open a file by using File open/save dialog).
- Directory will be always set on the path that you provided in the box underneath.