He is weak till 6, but getting stronger as game goes on. Your E has very good potential, like as cancel sylas Ult steal, Sett R canacel or Garen R immune etc.
You can use your R not only for offensive also for defensive like, run from multiple enemies to alone one or help your teammates for escape to blind enemies.
Very strong Tank/Bruiser destroyer. When fed you can do anything, wins (nearly) every 1v1.

Nocturne isn’t a farm bot. He’s a precision weapon – a tool of fear and burst. You’re not just a jungler; you’re a hunter in the dark.

If u starting blue side (Bottom) go: Red Brambleback -> Krugs -> Razorbeaks(Raptors) -> Wolves -> Blue Sentinel -> Gromp -> Scuttler Crab/Gank top/mid
If u starting red side (Top) go: Blue Sentinel -> Gromp -> Wolves -> Razorbeaks(Raptors) -> Red Brambleback -> Krugs -> Scuttler Crab/ Gank top
You can do reverse clear if pathing to enemies without flash

You are expected to play alone. At least, this is what I do. I cannot count on my allies to do their job. I will do it for them.

Early

-Always do full clear, after search for ganks if possible
-Farm until 6
-Someone overextense? Ult for kill

Tip: Do not force ganks if you cant secure kill, flash isn't enough. Better go farm and be patient for their mistakes.

Mid

-Counter gank with your Ult
-Take objectives (in lower ranks drake> herald)
-Track enemy jungler. Really helps if your team is blind
-Do not teamfight in disadvantage, if your team wants spam them to not

Late

-In teamfight ult for backlane to hold/kill them (GA is very helpful bc if u die you can respawn)
-If u won teamfight go do baron
-If u can siege any tower, ask your top laner to do it and hide in ult range to eventually help him(meanwhile you can do camps but be aware for your ult range)

Standard Combo
R -> Q (in dash) -> AA -> E -> AA (use W if he want hard CC you)

Pre-Ult gank
Q -> AA -> E (follow when feared)

Dive concept
R -> Q -> E -> AA -> W

-Fog of war is your friend if they don't see you they dont expect you
-Be decsive, If you R there is no coming back
-Play for Tempo. Farm -> kill -> reset -> farm -> kill
-Don't waste your ult its your main way to be effective in game.
-Build with brain: Edge of Night on 1 spell CC, Serylda for armor stacker, GA if you really fed.
-Ult before doing objective to slow down engages from enemies
-When Ult prioritize:
1. ADC
2. Mages
3. Solo Splitpushers
4. Support if it is enchanter
-Don't think much about using your ult to make pressure on enemies, cooldown is low
-Prioritize gank lanes without dashes (Jinx, Syndra, Olaf)
-Before Ult sweep vision, element of suprise is a key
-Don't overgank early you will lose tempo, except for ganking low Health enemies

One kill can win game, dont rush without mind
Gank mid often. If you kill on mid whole map is easier to control
My personal favourite: Mute all chat if ahead, people will make you play aggresive and without mind.

It is important to stay alive as jungler because it is the most tempo heavy role the second you die it relieves all pressure on the map and allows enemy laners to play over aggressive, the enemy jungler will also punish you hard and make it hard to come back. This is especially important during objective timers because if you die the enemy can force a baron without any threat of smite steal.
Staying alive as the jungler creates almost as much pressure as ganking, it is very important to not show on the map or not gank unless it is valuable enough to do so. the second you show on the map it relieves all pressure off laners and they can go for aggressive plays they normally wouldnt if they didnt know where you are