I’ve been a fan of Joe York since first getting introduced to his SaaS Rules of Thumb mathematics a few years ago. Start with SaaS Metrics Rule-of-Thumb #1 and read all 10 rules. It gets a little deep, but be sure to at least come away with the concepts and relationships. These are must knows around which to build successful software strategies and profitable businesses.
If you are familiar with his work, start anywhere in his chaotic-flow blog to continue to reap knowledge from his experience and insight.