I haven't found a build that's worked better than this for me. I believe it to be one of the most if not the most effective for Nocturne. One thing that you always need to remember when you're Nocturne is that you're an assassin. Not a bruiser and not a tank. Don't initiate and back out if it gets to dangerous(you're useless if you feed). And Please read the whole thing before you rate =).

For runes I take Armor Pen marks for good damage output easily best for Nocturne. Flat mana per 5 seals so that you can spam your spells more early game, I think that dodge seals would work fine too. Attack speed glyphs for help early and late game so you can kill fast without having to buy attack speed items, an alternative could be cooldown reduction. Lastly I choose armor pen quints for the same reason as the marks, flat help quints would work well too but at a lack of damage.

Masteries I go a standard 21/0/9 build grabbing one point in extending buff durations. If you play well you don't need to go down the armor path but if you're new you can, It's just not my cup of tea.

For items I grab a long sword and a health pot before i leave. I farm and usually get first blood so I can go back and finish the brutalizer and if possible buy lvl 1 boots. Next trip back I get berserker greaves or if theres a lot of cc, merc treads. Afterwards I get a vampiric scepter for life steal, but if I have enough I grab a bf sword. By mid game you should have finished your blood thirster and have part of your phage made if not already completed. I immediately follow up with a frozen mallet for the nice slow and health. Now I build more defense with a banshee's veil as the health, mana, and passive are all perfect for Noc. By late game you should be working towards your Infinity Edge or Madred's Bloodrazor depending on how tanky the team is (I almost always opt for the Infinity Edge)

I lvl Q first for the harrass, speed boost, and damage. I then get my E for the fear and can usually get first blood with these two skills. I try to prioritize so that q is one level above E and W is one level below E. W is an important skill but doesn't help get kills as much as the others.

I grab ghost exhaust as the speed boost combined with your Q can escape or chase extremely well and exhaust helps with both.

I've played Nocturne for around 2 weeks and while I haven't played him heavily I believe he's easy to play as long as you know when you can kill. I've never had a negative game with him and I usually end up with kills above 10 deaths below 5 and assists above 7. Any and all comments are welcome please and rate and tell me if I can do anything better be it explaining or changing items.