1. Governments (should) exist to improve the welfare of their citizens and protect the citizens from predictable and preventable threats while preserving individual rights.
2. The definition of "welfare of their citizens" and the right balance between protection and individual rights are debatable points that should be settled democratically, within the boundary of certain rules.
3. Boundary rules for #2: all people should be treated equally by the government, and not subject to punishment or restriction of rights OR significant unfair advantages for factors that are beyond the individual's control, except in extreme cases of threat to other members of society. (The exception takes into account things like locking up drunk drivers, for those who subscribe to the common theory that drinking is beyond the alcoholic's control).
4. Number 1 requires the establishment of rules that may seem to infringe on the "rights" of some citizens, and these should be determined democratically, within the boundaries described in #3.
But what really makes me a "progressive":
5. Changing the rules will almost always cause significant upheaval in some people's lives - as commonly said, there are winners and losers. People should not be drastically punished for playing by the rules of the games within ethical boundaries that they were raised to believe in. (Edit to add: the boundaries in #3 require this.) And regardless of the "should", the fact is that rapid, draconian (to some) change will usually cause backlash, that will often reverse the positive social change that was intended, and create cultural divides. Therefore progressive change (slower, more incremental, more compassionate to all) is preferred to radical change.
My definition of "progressive" is not that of the current "progressive" movement. Most "progressives" I've met are actually radicals but don't want to call themselves what they are. They want overnight change in all things, not caring about how that will affect everyday people caught on the wrong side of the issue, or what might happen with the backlash. (I am not talking about gay marriage here, by the way. Civil rights come under #3 and are more urgent to deal with, particularly when few if any people of ethical behavior will be hurt.) So, I don't usually call myself a "progressive", because I don't want to be identified as a radical when I'm not.
I usually just call myself a liberal.