Starter items

Core items

Offensive items

Strengths
Nightmare Robin, a great assassin who jungles very well with aoe dps, high burst damage, a blinking ability to target enemy mob or ally, and an ultimate that tears through most champions. The first thing you are going to want to do is read each of his abilities, and understand their strengths. You should notice that most of his skills do not apply a high percent of attack damage, but will discover the high output from his W skill and his R skill (ultimate).

Weaknesses
Due to the low percent damage provided by Nightmare Robin's skills, his burst is very low early game. It is mandatory to choose your targets wisely. Do not jump into every fight you see. It is best to trap your opponent in jungle by coordinating wards (surveillance cameras) to monitor your enemy jungler's health and position. Also, without sufficient lifesteal, robin can lose out to most AD carries and fighters early game. If Nightmare Robin is caught out of position, or without his E skill, he will more than likely die. Stolen powers typically provides enough escape for Nightmare Robin in my following explanation.

Stolen Powers
Nightmare Robin's X-Ray Vision - Utilizing this skill allows you to pump your dps by 5% for added damage output during ganks, as well as, preparing lane ganks and jungling presence. I often find myself using this skill to monitor larger areas in the jungle lanes, tracking enemies who retreat in the jungle, gaining vision in stealth nodes (VERY IMPORTANT), and added vision in critical ganking spots near lanes. Many spots in lanes have thin barriers that allows Nightmare Robin to get relatively close to your opponent to use your E skill, allowing you to dive for fast W and R skill smashing. The cooldown is also a great benefit, as you will have it up every 100 seconds.

Gaslight Batman's Surveillance Cameras, or Robin's Surveillance Cameras - Both very strong, and necessary to control your jungle, as well as, to utilize for escapes. These cameras cover much of the jungle, providing 2 possible allies in the jungle as targets for your E skill to escape. I find myself caught in the jungle from roaming players and use obstacles to place my cameras over, and than blink to with my E skill. The ability to stick your camera in a stealth node area that is near your enemy jungler's relay or creep spawn is also a must. Many times, junglers start in bottom drone pack x4 by bottom lane, and quickly getting to the stealth area with a camera is a great way to steal last hits, apply extra damage, and harassment on your opponent. To get the best advantage of this at the start of the game, sit at the edge of your spawn point until 0:04 seconds until match begins, and than run to the barrier that stops you from entering lane. Immediately race to the drone spawn x4 on your opponents bottom jungle. If done correctly, you will utilize the full advantage of your added sprint from your spawn point, and will cover the most ground before it wears off.

The rotation being used on an enemy player is based on the situation:
Ganking from stealth node
I open with my Q to stun the target, or to steal a creep kill when my opponent is jungling. I then follow up with my E to dash to my opponent, allowing myself to attack normally. Once my initial auto attack goes out on my opponent, or his jungle target to steal the kill, I then immediately use my W to trigger an immediate cooldown on my auto attack, attacking either the player or jungle target to secure a kill. If my opponent is weak, I will save my R until my opponent is about 30% health. The less health my opponent has, the more damage I can do with my ultimate (R skill). Note: Ultimate can not target jungle creeps / Doomsday Device / Raider.

Escaping
Placing cameras over walls in jungle or in lane so that you can target it with your E skill. This is great for engagements and escapes.

Amplifiers
The amplifiers should be self-explanatory. Each one is provided a larger amount of cooldown reduction per level, movement speed, and some added crit damage. These arent as important, and can be adjusted as you see fit. I have found that the added damage amplifiers arent that effective, but cooldown reduction and added crit damage is the better of your choices.

Items
The starter items are self-explanatory since you will be jungling, and need both damage and lifesteal.
The core items are necessary to allow you to jungle with high health, put out hit burst damage, and increase the chance to crit. The belt is absolutely necessary to destroy your opponents with high burst. Do not miss getting this item on either your first or second core item. That means build it immediately or just after building soultaker katana.

Leveling
Level your abilities in this order: R > W > passive > Q > E. This will prioritize high burst damage, high passive damage with attack speed, added dps with your Q, and finally a lower cooldown on your blink.

Jungling Route
I suggest you develop your own jungling route, but i start with the bottom drone group x4 near bottom lane, than moving to the drone group x2 near your base. After defeating them, I move to the top drone group x4 near top lane, while monitoring the enemies for potential ganks. If I dont gank the lane, i move to my opponents drone group x4 in top lane to either see if they are there, or to drop a camera to either steal the kills or wait to ambush my opponent. This rotation is pretty good for gold, jungle control, and keeps you relatively close to relays for immediate capture. Always attempt to capture you opponent's relay first if they are out of position, such as pushing a lane too far, engaging in a lane fight, or if the jungler is clearly out of position (bottom lane, top lane, or dead).

Casting
As a final thought, take the time to practice instant casting. Don't use point and click casting, or shift casting, as that delays your ability to jump because it creates more time between clicks, targeting, possible movement of your mouse, and a delay on camera placement. The camera placement and E skill, if done very quickly and accurately, will allow you to jump immediately away from your opponent, often times escaping. If you dont utilize the instant cast, you will more than likely suffer from the delay in key strokes and will jump a relatively small distance that is ineffective for escape.