Cambridge has provided a complete practice test with answers for you. The audio files for the listening are included in the .zip file.
Download a full test here
Click on the text “Download sample papers for Cambridge English: First”, you can find it just below the line that says “Free support materials”. Below the link to the practice paper test, you can even find instructions on how to try the computer-based test. Good luck!
Don’t forget to check my tips for each section of the Cambridge English: First exam