However, there is a gentle art to reading primary source effectively.
Everyone who writes, writes for a purpose. Discovering that purpose is not only part of learning about the era, it's also necessary to read between the lines. The simplest stuff would be letters written to inform personal friends and family, though even there agendas can get in the way. Diaries may be a form of soul searching; early Soviet Union diaries are often relentless attempts to transform one's self into a New Soviet Man, and one diarist, having written on her engineer husband's meager office, hastily added that she wrote it so that future generations will know what sacrifices the first generation made for them.
Polemic survives in great quantities -- well, relative to the total surviving quantities -- and that's all axe grinding. What really gets fun is when you're trying to construct a world, and you have to remember that nothing gets attacked in polemics unless it was defended. That the Art of Love attacks the notion that marriage is compatible with courtly love with such fervor and at such great length shows that the notion sprang up very quickly, even though we don't have written records till rather later.
Etiquette books, of course, describe what ought to happen. Which is valuable information in itself, telling you what they thought. But for what really happened, they can only given a vague guide. What is passed over briskly is probably implemented. It's when a guide prescribes at great length, and with supporting arguments, that you know it's often defied. And, of course, if behavior goes unmentioned, is that because it's utterly acceptable, or so unthinkable that the writer never dreamed of forbidding it, any more than he would write that it's rude to breathe underwater?
Laws have the same effect. Many Muslim countries had laws against freeing slaves who could not support themselves. You will not find such laws in the antebellum South. Fortunately, there you have much polemic, and one charge the Southerners brought against the Northerners was that their menials were much better treated; a factory owner would fire a worker as soon as he was less productive, while the slaves had their masters to care for them in old age. And perhaps even more to the point, you don't find any abolitionists offering the horrible state of such freed slaves. Then, if a law exists, what does it mean? Is it a dead letter, or at most a slap on the wrist for the crime involved? Was it passed after one, never repeated outrage, and prohibits behavior that never occurs? Or does it show that a behavior is habitually committed, prosecuted, and punished? Prosecution records are more useful for the last, and for the first two -- well, sometimes you have a hard time finding out. Even in real life -- in Victorian England, a man, accused of murdering a woman, challenged the accuser, her brother, to trial by combat, and having appeared in armor and the other man not showing up, claimed he had won his case. A lot of laywers hunted through a lot of books before they concluded -- well, he had, trial by combat never having been officially repealed.
The safest thing in any document is that which is not the points they are trying to make. Metaphors, for instance. When Saint Augustine, discussing a theological points, compares it to a betrothal, which lasts a year or two so that the bridegroom will not hold the bride in contempt, having gotten her too easily -- well, you know how long Romans expected betrothals to last, and the reason why. Other incidentals also can appear that way. A rationing law in Puritan New England banned cakes, pastries, etc. etc. -- except bridal cake. Since the law was clearly not written to express the importance of wedding festivities, it's very clear evidence for it. Similarly, when an ancient Athenian describes how his opponent had actually broken into the women's quarters in this man's home, and all the women there were shocked and horrified, being unaccustomed even to seeing their own male relatives, and some of his neighbors intervened at this outrage -- whether that man did what was claimed is one thing, that his prosecutor thought the jurors would regard women who seldom saw even their own male relatives as particularly proper women is another, and quite clear.
But even when not telling with much of an agenda, there is always the matter of what to write about, and the rule is that one writes about the exceptional. When Henry VIII was reputed to have said that the midwife should save his son, not his wife because wives were easily obtained, it was spread because everyone agreed it was outrageous behavior. (Evidence is that the midwife made it up some time after the death of Queen Jane, apparently to summarize his attitude. And one notes that his next two efforts to obtain a foreign princess in marriage were rebuffed by the women in question, who explicitly told the ambassadors that they thought it hazardous to their health. But I myself have read writers who took it as obvious evidence of what men thought about women then.) One meaning of the "exception proves the rule" applies here: if a woman notes in her diary that she was up at 6 on a given day, it probably means that she wasn't, on other days where it was not noted. Alas, you can not count on her having such a day, or the equivalent thereof in other works.
Traveller's tales are sometimes useful because what is ordinary in a region is extraordinary to the traveler. On the other hand, his exposure to the region is small and probably unrepresentative, he can easily misunderstand, and he has, generally, much to gain by lying and little by telling the drab truth. Particularly dangerous are salacious or shocking tales.
Good secondary sources, the sorts that historian write for each other, or at least not the completely uninformed public, are often a help in this because they discuss documentary evidence and read between the lines. A discussion between early Christian bishops about whether baptism should be withheld until the eighth day is evidence that the Christians baptized infants.
But there's no real substitute for reading primary source to learn how to do it.