Lucian Gameplay

Whenever I play Lucian , the same thing happens. I get ahead in lane (my score is normally close to 3/0/2). I am also generally getting equal farm to my lane opponent, and by 30 mins in I'm normally ahead even further. However, once the 30 minute mark passes, I suddenly find our team losing fights, skirmishes and objectives, and I don't know why. My positioning is pretty good, and I can get good damage off, but my team still ends up losing the fight. Maybe I'm ulting too early or too late. Maybe I'm going to aggressive or too defensive. Or is it just my team the causes my 29% winrate on Lucian (pretty terrible). Idk. All I want is some tips on how to play out teamfights (or just how to play the late game) as him.