One word: people. A startup can measure its progress by looking closely at both the employees they have attracted as well as the people they have the opportunity to do business with. We find this lens to be the primary indicator of all things that mark success and progress within a startup, both short- and long-term.
So, what makes an employee "good" for a new company? Each startup has its own distinct needs and culture but generally, they should be people who take initiative and move things forward, ask questions, bring new ideas to the table, and willingly jump in when a colleague needs help. Pull together a few types of these employees and you'll have an engine that can take you places fast. A "good" client treats you as a valued partner, conducts fair business dealings, defines clear expectations, and communicates disappointments.
Lastly, every entrepreneur should gauge progress by asking themselves if they are more fulfilled with their new endeavor than in their last role. Again, we bet the answer will be directly linked to people.
If you were to analyze 100 startups, you'd find a direct correlation between people and the markers of company success, including: sales, products, teams, and culture. When your vision and mission attract good people on both sides of the equation, take it as a key sign you are on to something.