Nocturne will look to power farm early so he can get level 6. Try to invade him and take away his camps to delay his level 6 power spike.
Nocturne has strong dueling potential if his fully procs on to a target. If you are dueling him, try to create a gap when he casts his on you so you do not get feared. Re-engage once it’s finished.
Nocturne will try to get ahead early by ganking lanes that are immobile or are over extended. Try to track him in his jungle and counter gank lanes that are being ganked. If you cannot counter gank, try to gank a seperate lane or steal his camps.
In the mid game, never split up and do not go alone. Nocturne will look to pick off targets that are alone and assassinate them. You can completely stop his win condition if you just group.
Whenever Nocturne is split pushing on the other side of the map, he has no way of getting to his team or helping them. If you see him somewhere else, look to engage and start a team fight.
Nocturne will try to take down the squishiest high priority target at the start of the fight. This is usually the Mid or ADC. Clump together in team fights to reduce his one shot potential.
Nocturnes major power spike is at level 6 when he gets his . Try to delay his power spike by putting him behind early so his level 6 is delayed.
During the late stages of the game, Nocturne will pick up Guardians Angel. If you can take down his Guardian Angel, he will not play as aggressive in team fights. When his GA is down, look to burst him down once he engages.
Once Nocturne has completed his first assassin item, he will deal a lot more damage. Pick up health and armor items to protect yourself from his burst.