It really depends on the course. For bio, physics, and gen chem, I found that the lectures and labs were concurrent and each really reinforced the other. I would definitely recommend taking these together. For orgo, though, at my school, the labs and lectures have zilch to do with each other and for some reason, the labs are *ahead* of the lectures. So I made sure to take one semester of lecture before I started the labs, and frankly I wish I could've had both semesters of lecture first.