mv this-is-a-really-long-filename this-is-a-really-long-filename.bak
mv this-is-a-really-long-filename{,.bak}

if you're typing a multi line command, instead of editing the line by going back and forth use the "fc" command to open the line in an editor

If you want to use the last argument from your last command press ctrl+.

If you want to use the first argument from your last command press alt+ctrl+y

You can use !: (word designator) to reference arguments from the previous command line. !:0 is the command, !:1 is the first argument !:2 is the second etc...

$ ls -l /
...
$ echo !:1
-l