A first mate ranks directly below the captain of a ship, and provides assistance to the captain. First mates work on cruise ships, fishing boats, cargo ships and other vessels. They assume control of the ship when the captain is off duty. Often a first mate aspires to become a captain, gaining experience through this job. First mates, captains and pilots of marine vessels earned an average of $61,960 in 2008, according to the Bureau of Labor Statistics.

Become a deckhand to gain experience. Learn first aid and firefighting skills as well as how to perform daily work duties during your training as a deckhand. Gain 1,080 days of experience. Alternatively, complete a three-year apprenticeship or attend a merchant marine academy. The U.S. has seven accredited programs as of 2011. If you have previous experience, consult the U.S. Coast Guard to determine whether you can use this experience to advance in rank.

Gain a Transportation Worker Identity Credential (TWIC) card through the Transportation Security Administration (TSA). Apply for a merchant mariner credential for third mate status from the U.S. Coast Guard. Pass a drug test and physical examination as well as an examination to test your knowledge.

Gain 360 days of service as a third mate, and apply for a second mate credential. Alternatively, if feel you already have the necessary experience, apply for the credential and complete the examination to become second mate. If you gain the 360 days of service and earned third mate status after February 1, 2002, you don't need to take the exam.

Gain 360 days of experience as a second mate, and apply for a first mate credential. Pass the exam to become first mate. Maintain excellent physical health and strong teamwork skills, delegating responsibilities to the crew in cooperation with the captain.