A note: plebs is the singular of plebs. Plebs is a collective singular that, outside of Archaic Latin, does not have a plural form, any more than populus has one.

"Improvement" is a rather vague concept. I'm almost certainly able to give you an answer to your question, since the urban plebs are sort of what I do, but as it stands right now it would be the subject of an entire study, much of which would be extremely speculative. On the one hand in certain respects the economic station of much of the urban plebs markedly improved in the early Principate, with the establishment of, for example, more rigid grain laws. On the flip side of that, Augustan grain distributions only benefited a small group of the population with no regard for who actually needed it the most. And of course there's the loss of what little participation in the political process the plebs urbana generally had to begin with. There are also things like the reinstatement of the collegia and other plebeian associations, but under much greater oversight than before--the collegia of the Principate were strictly scrutinized and watched over to the point of paranoia, and even the gathering of collegiati more than a couple times a month was forbidden. There's also an issue that, despite what Sallust and other educated Roman authors liked to think, the plebs or even only the plebs urbana, was not a united group. The plebs urbana consisted of freeborn, freedmen, and foreigners, who themselves might be skilled or (more likely) unskilled workers. The lots of those different groups were totally different--skilled tradesmen like shopkeepers or artisans might be a relatively comfortable plebs media, with their own permanent places of residence and a reasonably secure means of income, whereas the majority of the urban plebs were semi-itinerant day workers who lived a miserable hand-to-mouth existence. It's hard to speak of an "average" member of the urban plebs.

A little more precision would be nice, otherwise the solution is basically to throw books and articles at you until you're ready to be a scholar on the subject in your own right :/