The road to becoming an airline Captain starts long before you get hired by an airline. You should start planning on earning the left seat in the same way you plan a cross-country flight:
SELECT YOUR DESTINATION. This might be the left seat of an airliner, a business jet, crop-duster, whatever. Know where you want to go, and, just like on a cross-country flight, you may have to divert around unexpected weather or even land at an alternate.
CHECK THE WEATHER. Be aware of conditions along your route and at your destination, and be sure to check NOTAMS. In this case, learn about hazards along your route and be ready to change destinations (airlines) if conditions aren't favorable.
CHECK THE DESTINATION FACILITIES. Just like knowing your airport destination runway lengths and widths, elevation and available services, you should know what the airline expects of its pilots. Specifically, airlines are VERY conservative, and plan ahead to not have ear-rings for men, visible tattoos, or extreme appearance. Get that degree to make yourself more competitive.
KNOW THE MILESTONES. Just like checking your visual check-points along your route, plan ahead for the ratings you need.
CONFIRM YOUR LEGALITY. Make sure you have the certificates, and the medical, you will need for the career. It would truly be a shame to spend many thousands of dollars on ratings only to then discover you have a disqualifying condition, such as color-blindness.
CHART YOUR PROGRESS. Keep track of your progress along your journey to a professional pilot job.
BRIEF YOUR APPROACH. Be totally ready when you are called in for an interview. That means having your appearance exactly as you want it, including an interview suit/outfit that fits perfectly. Read Molloy's Dress For Success and Molloy's-Live For Success.