Nocturne usually doesn't go mid but I thing that picking on the lower life champs is a advantage for noc...

Nocturne is a wonderful ganker as we all know... so when entering mid try to get in the brush.

Alright how about this, Nocturne will first get Duskbringer. So when going to mid try to stay in the middle of the lane, then as your enemy champion approaches dusk bring them when they are in the middle of the lane by pulling them in. Then use Ghost and Exhaust on the champion while on top of the path from Duskbringer. You should then kill them if they are 600 or below max health. Recall after that and try to level to at least 3 having a upgraded Duskbringer and having a Unspeakable Horror. Next kill will be a gank.
So when entering mid go to the side and trough the jungle. On your way you can kill jungle mobs. When you get to mid get inside the brush and wait for them to get close to your turret. Then use Duskbringer on them and charge. When you are next to them use Unspeakable Horror and fear them in turret range with them at low health. They should die but if not, chase them with the time you have. Then use their death to your advantage... level up as high as you can and I am guessing at least up to 5. You will have Shroud of Darkness and a upgraded Duskbringer. When they come pull them in by pretending they could easily kill you so give them a little shot at you to lower your health (and If you aren't doing good this far dont let them get shots) after your health is low you want them to be a little bit further than the middle of the lane. After that use Duskbringer and ghost to catch them. After you are hitting them use Unspeakable Horror to fear them away from leaving, at this point use Exhaust and Shroud of Darkness encase there is a stun or slow power they have. Then kill them.

When you hit level 6 you want to make sure you wait for your enemy champion to get near the turret. Then put you cursor on Paranoia and wait till they are inside range then BAM! Right into them using every power / ability you have killing them. (If you dont kill them charge and follow them, if Ghost or Exhaust is ready use that.) By now you will have a great amount of kills with NO DEATHS hopefully. Now you can go in the other lanes for open kills, and ganks.

If you get a nice amount of kills repeat everything I have said in this chapter and have happy ganking! :)(Also you summoner powers can replace Ghost with Clairvoyance)