The first thing is planning. Sit down, Write what you want to accomplish. Design in other words. Then the next step is developing, Finding the crew to make your game come true. Coders, Artists etc. The last piece is bringing them all to together and managing a team of individuals to get this project ready for release. Doing tests over tests, Wasting countless hours into figuring out issues that came up because of your new patch 
But the most crucial thing i was taught is that when you develop a game, Don’t do it for profit alone. Do it for people. Something that others will have fun with, Dark souls 2 does that in it’s own way with countless deaths. Infamous does that with all those powers, Graphics and some really nice story. And so forth.