Well it really depends. The first 1-2 weeks of a sport (any sport...baseball, NFL, NCAAF) can be insanely off. This is where I usually make my money only to give it all back later in the season (I'm up 400% of my bankroll right now since the season began....)
Usually by week 3 it's pretty clear how good a team is or isn't, thus the lines get a lot tighter and games end closer to predicted spreads. In all honesty, setting and predicting what a line will be is pretty easy once you've become a seasoned gambler. The difficult part is knowing which side to play. I'm scared to death of my bets this week but I'm gonna try to have one more winning weekend before cashing out the lions share of my account. Fingers crossed!