Alright, let me set the stage for you. It takes about 3 camps to get 300+ gold, and if you take Krugs it only takes 3 camps to be level 3. On the enemy team I see a Predator Skarner, a champion with fantastic AOE clearing ability, who wants Boots as early as possible to unlock and utilize his Predator. Knowing this information, what route does Skarner take? Or even better, which Buff should Skarner be starting at?
It appears to me that a lot of Junglers these days aren't familiar with the 3 technically 5 Jungle routes. This is fine if you know just one or two for your particular champion but it does no good when you start to apply the wrong routes on the wrong champions. Kayn loves to start Raptors, leashless even because it's so easy for him, but try that with Warwick and yeah, have fun with that. I think it's probably one of the most important basic principles that Junglers should learn to improve their macro game, early game, and general performance in the Jungle. With that said, what are the 5 Jungle Routes?
Lv3 Ganking Route:
This is the one _everybody_ knows. Start at the buff opposite of the lane you want to gank, clear it, Raptors, Wolves, and the other buff for a 4 camp Level 3, and a gank window of just around the 3 minute mark depending on how fast you cleared. If you can't clear Raptors early, do Gromp. This should be the first route every Jungler should learn and master. However, it should never be the only route you know how to do. Even if your champion is rather hard locked to this route (Single target Lv3 Junglers like Warwick or Lee Sin), the biggest weaknesses of this route is its predictability and inflexibility. Especially as you go against Junglers who understand Jungle Routes and Counter Jungling/Ganking, your obvious gank windows will end up getting you killed if you fall for the other Routes' counters for you, that or you'll have all your camps stolen.
Lv6 Farming Route:
This is the one that makes all three of your Laners hate you no matter what else you do for the rest of the game. Also not rocket science, start at a Buff, go to Krugs or Gromp, and just sweep all the way across the Jungle. If you can get two Crabs, you can hit Level 6 in just two clears and a touch of stolen experience while doing Raptors. Many of these Junglers can just about get onto the River just before the 3:30 mark, meaning that they will fall behind to faster Lv3 Clearers if they go straight for Crab instead of Ganking. This route should obviously be reserved for Ult Reliant Champions or late game Hypercarries.
Lv2 Aggro Route:
If your Champion is particularly stronger than the opposing Jungler at Lv2, or you have an extremely strong/volatile Lv1 laner, you should start Red and immediately move to Gank or Invade the enemy's Blue. This route has lost a lot of power since Scuttle Crab spawns moved back, but on the bright side, this means not as many people are warding to defend from this. Note that unless you're playing a champion who needs to gank right away (Shaco, Twitch) this should be considered more in the form of calculated aggression than a cheese strat to abuse. This means to be perfectly ready to Vertical Jungle, keep a close eye on your laners' Lv1s, and knowing how to fight the enemy Jungler or what to do if you run into them. The best examples of these types of Junglers are Jarvan and Xin Zhao, with champions like Kindred holding this route in their back pocket in the right matchups.
For those who answered Reds/Raptors/Krugs earlier, this is it. Clearing these three camps immediately grants access to both level 3 and Boots. If you recall right away, you can clear one more camp before Crabs spawn or immediately Gank with Predator. Clearing Raptors first also means that, after you gank and/or secure Crab, you can rotate from your Blue/Gromp/Wolves and Raptors should just about respawn as you get back into your Red Side Jungle, efficiently transitioning from a Predator Gank into a full clear. Obviously, any Jungler that runs Predator should keep this route in mind, however many Tank Junglers like Amumu, Nunu, and Rammus love this clear as well. This route is also the natural route for Leashless openers, Kayn being the star example of that idea.
This route first popped up in the Lv2 Scuttle Meta as a way for Level 3 Junglers to counter the Lv2 Meta. By starting at Red and then immediately moving to Krugs, while warding the opposite Pixel Bush, this allowed Junglers the ability to take their time and see if the enemy Jungler goes straight for Crab or a Gank. If they do, after clearing Krugs, you can immediately invade their unprotected Blue. Otherwise, this gives an opportunity to Lv2 Gank the Side Lane if your champion is capable of doing it, or transitioning into Raptors. In today's Level 3 Meta, this route will let you gank Mid first, which is key to taking control of the Scuttle Crabs. On the other hand, even if you can't gank Mid, you still have an easy opportunity to transition into full clearing if your Champion is okay with that, or routing to the opposite Scuttle Crab with plenty of time to heal up and contest. Unlike Single Target clearers, this Route's strength lies in just how wildly flexible it is.
I highly suggest that every Jungler should take a minute to look at their top Jungle Champions and consider which route their champ best utilizes. For you newer guys, this is required knowledge before you hop into the Jungle. For the older Junglers, I realize the Jungle has changed a LOT, many times in a row, but at the very least you should keep up with the basic routes to stay competitive in the game. In the future, I would love to go into deeper depth on how these Routes all interact with each other, but for today, I just hope that Junglers learn these critical basics to their Role.