Founder PRECOIL, I advise Silicon Valley startups & corporations on product strategy and business model innovation. Formerly Neo, BigVisible and various startups.
The software development life cycle, traditionally, was mostly based off of Winston Royce's whitepaper: http://www.cs.umd.edu/class/spring2003/cmsc838p/Process/waterfall.pdf
Unfortunately, much of what he wrote was misapplied and became a series of phase gates and check points.
Today, most of what you'll see from a software development life cycle is loosely based off of the Agile SDLC: http://agilemanifesto.org/
Basically concept, sketch, build, and test iteratively.
Actually, old school custdev from Blank's 4 Steps to the Epiphany goes a long way here.
Take the time to identify and design your strategy for:
The challenging thing about the Fortune 500 is that you'll meet several people who have the power to say no, but not many who have the power to say yes.
Retention. It's the guts of your product. You'll not be able to solve for churn without first understanding Retention. It most likely also influences your Engine of Growth and your Acquisition spend. I recommend designing experiments to explore and learn about Retention before you mistakenly invest in scaling the wrong thing.