The starting point for assembling daily fantasy lineups is always the point spread. For one, it tells us which games the oddsmakers view as high scoring and which ones they believe points (and fantasy points) will be scarce.
It also gives us an educated view of how the game will play out. For instance, when one team is a significant favorite, that indicates that for the last quarter or so of the game, the team that's leading will probably be handing the ball to the running backs to run down the clock.
On the other hand, a game that's a pick 'em but has a high over-under number should be one in which both teams will be airing it out and the quarterbacks and wide receivers should enjoy productive fantasy days.