The facts are is that we know very little about pre-Christianity Slavs. What little we do know is from Christian sources and, sadly, they're very biased against the Slavs. However, it's highly unlikely that they were as barbaric as they were depicted. As for the common people, very little would have changed for them, even over a two-hundred year period. In fact, many peasants would have been pagan for generations after the "christianisation" of the Slavs, since Christianity was enforced from the top down.

We know really, really little. First of all, pre-Christian Slavs were illiterate and therefore left no documents of any kind. This means we are limited to external sources like Bavarian Geographer, On the management of the Empire, Leo the Deacon and Abu Zayd al-Balkhi.

Second, wood was used as the main construction material and modern archaeologists find lots of embers and rotten logs instead of ruins and runestones. We know, for example, that a typical house of Prague-Korchak culture was a semi-dugout, but we do not know who the tribal leaders were, if they were elders or warriors, or if their houses were decorated in any way (Source: A.A. Gorsky)

This is a very fraught question. It's not even clear exactly what material culture(s) was (were) associated with early Slavic speakers (henceforth, "early Slavs", though the reader should not read into the phrase any sort of concrete Slavic "ethnicity" or "people"). We can say confidently that early Slavs were not engaged in seafaring: *marje 'sea' is the only sea-related word of Proto-Slavic, so far as I know. The most credible Slavic homelands are all decidedly inland in Eastern Europe, with most linguists preferring to place the Slavs in the Dnepr basin.

We have a bit of testimony from the historian Procopius (writing in the sixth century), who says of the Sclaveni and the Antae (who we may reasonably assume to be Slavs) that they had some kind of democracy, and were not led by a single man but made their decisions as a group. He reports that they live in "pitiful hovels" and that "every man is constantly changing his place of abode". We have some archaeological evidence of small settlements based around poluzemljanki or 'earth-floor houses', that housed nuclear families. As these families grew, members would move out to new locations several miles away.

We have an account of the invasion of the Balkan peninsula from John of Ephesus (writing in the late sixth century), who reported on "an accursed people, called the Slavonians", who managed to overrun the cities and forts of Greece and Thessalonia and Thrace. He claims that they learned "to fight better than the Romans".

Emperor Maurice's Strategikon (also from the late sixth century) mentions the Slavs and the Antes, noting their fierce independence.

They are populous and hardy, bearing readily heat, cold, rain, nakedness, and scarcity of provisions. They are kind and hospitable to travelers in their country and conduct them safely from one place to another, wherever they wish. If the stranger should suffer some harm because of his host's negligence the one who first commended him will wage war against that host, regarding vengeance for the stranger as a religious duty. They do not keep those who are in captivity among them in perpetual slavery, as do other nations. But they set a definite period of time for them and then give them the choice either, if they so desire, to return to their own homes with a small recompense or to remain there as free men and friends.

Here we see an interesting account of the Indo-European respect for the relationship between guest and host. Also of note is that Slavs did not keep their slaves in bondage forever. It has been suggested by Horace Lunt that this particular tradition was integral to the success of Slavic in Eastern Europe.

Maurice also reports that the Slavs lived in wild, distant, and remote places, "like bandits", and were adept at ambushes and raids. They were also accomplished at crossing rivers, and appeared to feel quite at home in rivers generally. The Slavs were apparently averse to giving open battle.

Our picture of pre-Christian Slavic society is, as others say, woefully incomplete, but not hopelessly. We can say with some confidence that (early) pre-Christian Slavs did not live in large cities of their own construction, and especially early in their history, they did not seem to have many large settlements at all, preferring instead small and sparse earthen dwellings for a single family. They lived inland and were not seafarers, though they had an affinity for rivers. They did not have monarchs, or any solid governmental structures of their own, though they did co-opt such things when they were imposed upon them, as they were upon the Moravians by the Avars, upon the Slavs of Thrace by the Bulgars, and upon the East Slavs by the Rus'.

Edit: Oh! I don't have any quotes about this, but we are reasonably certain that the early Slavs practiced some basic subsistence agriculture with the *ardla 'ard, scratch-plow' (mod. Russ. рало ralo, mod. Pol radło). Somewhat later, after the change of Common Slavic *ū to *y, they began to use a plugъ 'plough, turnplow', a borrowing (both technological and linguistic) from Germanic-speaking neighbors. The turnplow seems to have allowed for the Slavs to begin their incursions into the Balkans.

If you're interested in learning more, I'd highly recommend Schenker's The Dawn of Slavic, from whose first chapter these quotes were extracted. It won't reflect the most recent work, but it's reasonably up to date and incredibly comprehensive, if a bit of a slog. Do let me know if you have any questions; I'll answer what I can.