You have to figure when Sin showed up, humanity had already reached a point of technological and warfare advancements. At the beginning, they most likely tried to fight Sin head-on. Finding that ineffective, they switched to appeasing the beast by casting aside most of their arsenal, withholding enough to protect the people and drive Sin away from heavily populated areas. Luzzu, a member of the Crusaders, tells Tidus how they've steered Sin away from towns many times.

Chances are, next to the summoners using the Final Aeon, survival tactics didn't evolve much past simple diversions to draw Sin away from the towns. Also, Spirians learned not to gather in great numbers. Heavy populated areas such as Luca tend to draw the attention of Sin, than smaller areas like Besaid.

Now in terms of Sin making a conscious effort to limit its attacks, that is very likely up until a certain point. When (SPOILER)Jecht became Sin, he made an effort to quell his wrath by listening to the hymn. He also made conscious decisions to show Tidus the atrocious power behind Sin. If Sin was entirely absent-minded and driven by the sole purpose of destruction from the get-go, it's likely that it wouldn't go chasing Tidus around Spira for a final confrontation nor would it try to calm itself via the hymn.

Since Sin is constantly reborn (SPOILER)from the Final Aeon, Sin's initial actions depend upon the fayth inside. However, the longer that fayth is Sin, the more it loses its essence as depicted by Jecht's failure to hear the hymn towards the end of the story.

In short, I believe it's a combination of strategy on the people's part and the will of Sin's consciousness that has allowed for people to survive Sin's constant onslaughts.