Controls
The controls are painfully simple: F sets up the Front Shield, while B sets up the Back Shield. Once engaged in combat, use Arrow Keys to move the cross bow cursor to target an enemy's ship and use Space ' to shoot.
Speed
As is the case with almost all 'arcade' sections of the Space Quest universe, it may be of help to lower your speed setting. As is the case with Astro Chicken, it's generally a good idea to keep it around 6, although the value may depend on the performance of your computer (or the settings of your DosBox).
Bottom Line
This is a very simple fight, and it should not take much of a learning curve to master. The only real "challenge" of this minigame is in tracking of the enemy ship, apart from paying attention to shields. Assuming your speed is set to a reasonable level, this game is trivial.