You need to change the naming format string in Options -> File Naming -> Name files like this to something like:
$if2(%album%,[Unknown Album]) - $if2(%albumartist%,%artist%,[Unknown Artist]) - $if($gt($if2(%totaldiscs%,1),1),$if2(%discnumber%,1)-,)$num($if2(%tracknumber%,1),2) - %title%
In addition to your basic naming, I’ve included defaults if the album or artist names are not known, as well as adding the disc number before the track number (e.g.: 1-02) if it’s a multi-disc album.
I hope this helps. If you have any questions about the scripting (link to the documentation is on that screen), just ask.