The Second Age was a period of change in Arda, but most of what we know about is Numenor and the lands west of the Misty Mountains. The Men of Darkness - those mortals who inhabited Middle-earth until the Numenoreans returned - are some of the least fleshed-out inhabitants of Tolkien’s writing. I’ve already covered them a little in another entry, but they deserve a second look. Rather than speaking in generalities, let’s look at the life of one man.
This is Eredan. He was born in an unnamed hamlet in the shadow of Mount Gundabad, east of the Misty Mountains, somewhere around SA 1000. His name is Sindarin, Ered-adan, ‘Man of the Mountains’ - though it is an inherited name, and he doesn’t know the meaning or origin of it. Racially, he’s part of the broad people of the Northmen whose horse-rearing segment ultimately became the Riders of Rohan.
SA 1000 is a volatile period in the history of Middle-earth. For the past 250 years, the Numenoreans have been exploring the western and southern coastlines, mostly under the command of their current king Tar-Aldarion (reigned 883-1075). Over in the east, Sauron has been slowly building his forces for the past five hundred years; around 1000, he finally has enough confidence to beginbuilding the Barad-dur.
On the other hand, the elven nation of Eregion is a thriving civilisation, and between it and Gil-Galad's Lindon, everything west of the Misty Mountains is inhabited by the elves. Greenwood the Great is also elven, and is several thousand years away from becoming 'Mirkwood'. Even Lothlorien - then known as Laurelindórenan - already exists, under a Sindarin king (probably Amdír Malgalad).
The Dwarves, too, are a strong presence. Khazad-Dum is a trading partner of both Eregion and Lorien, and its population is still swelled from the influx after Beleriand fell. Gundabad we don't know about for certain - it simply didn't get mentioned enough - but we do know it was one of the most ancient Dwarven fastnesses (and, in fact, the awakening-place of Durin the Deathless). Given the strength of the 'Good' presence in the West, and the fact that the Dwarves are, for once, friendly with the elves, it seems fairly likely that Gundabad is inhabited by Dwarves. The Grey Mountains, too, are said to have been 'long mined by the Dwarves' - they weren't driven out until the Third Age.
But then there's the north. This cold, barren land, the remnants of Morgoth's two bastions of Angband and Utumno, is known to be inhabited by the hardy, wandering Forodwaith, who at least are men. But it is also likely home to a whole bunch of nasty creatures: the cold-drakes who later conquered the Grey Mountains would have lived here, and it's entirely possible that the whole place was teeming with Orc warrens and Wargs. The land that would become Angmar is also very nearby.
So what, ultimately, does this mean for Eredan? It means a life in comparative safety, punctuated by short periods of terror when Something came over the mountains. It means the local friendly people are the Dwarves, who are notably secretive, and are probably only glimpsed occasionally (bear in mind that Gundabad is by way of being a holy site - they wouldn't be inviting in visitors, you know?). It means that there are constant, disturbing rumours from the south of the Men of Westernesse, who come in their great ships, cutting down the ancient forest, and while they aren't exactly out to get the inhabitants, they're not exactly here to make friends, either. It means the elves are a constant presence - but already slightly unearthly. Both the humans - who, 1500 years ago, stopped their march west and settled in the Vale of Anduin - and the elves - Silvan folk who halted in the same place even longer ago, led by the Sindarin King Oropher (who claims to have escaped from that mythical western land before it sank) - are 'backwards', never having lived alongside the Noldor or the Edain.
On the plus side, both Oropher and the Dwarves would have made some effort to teach the humans basic sanitation. Eredan and his relatives aren’t Edain - they don't have the extended lifespan of the Numenoreans - but he is still hale in his fifties, and his parents have lived into their seventies. They have a farm, and while Eredan still lived with them, his ‘job’ was to help tend it. But in his late twenties, he began to give heed to the stories he was hearing, by way of the Dwarves, or maybe the woodland elves - second- or third-hand, at any rate. Stories of the Numenoreans, about their encampments and their logging down in the south, and have him decide he's going to go and see them - or, more accurately, see what they’ve got that he could ‘borrow. Maybe even one of their legendary swords?
So he went south. He hiked down Anduin, passing by such places as the High Pass (and a party of Noldor from Eregion, tall and actually quite scary, with stars in their gaze...), and Lorien/Khazad-Dum, until finally he entered the ancient woodlands of the south (of which Fangorn is just the northern reach - but the Ents are a power in the world, too...). Finally, passing over open fields through what would later be the Gap of Rohan, he reached the river Greyflood, and the Numenorean city at Tharbad, or maybe the haven at Lond Daer...
... only to find that the Men of the West aren't even as nice as rumour would have it. They are, basically, stuck-up, convinced of their own superiority, prone to treating the locals as little more than slaves. And the worst part is, they're right about how much better they are... about all Eredan can do is get a job as a lumberjack (because the Numenoreans, they love their trees).
So now you have an angry, serious man with a knack for going unseen, in the employ of the most powerful nation in the world. And he's cutting down the ancient forests (which means he might well run into Ents), and he still wants one of those swords - and there's not really enough food in the work camps, and 'them in the city' have so much, they wouldn't miss a little…
And right there, you have the kernel of a story. Despite the lack of information about Eredan and his people, we can build an entire tale out of him.