Jungling is the act of killing neutral creeps in the forest from level 1. Why is this a good thing? It allows you to have two heroes soloing lane while the person jungling can gain experience and money by killing neutrals. Heroes such as Legionnaire, Tempest, Ophelia, and Predator are good at jungling, so use it to your team's advantage. To jungle effectively you will have to use creep pulling and creep stacking, but there is much more to it than that. Here are some guidelines of how to jungle effectively.
Rune Checking
2, 4, 6, 8, who do we eliminate?
Rune Checking is a benefit to having a jungling hero because sometimes they are able to check the rune if you have no wards up, and they may be the closest hero to the rune, stopping the other team from grabbing it. This is particularly effective against enemy teams which have a solo mid hero that goes bottle first. Stealing the hero's runes benefits both your team and yourself because if the rune is anything other than Invisibility, it can help you in your jungling.
Ganking Opportunities
Wait for it, wait for it...
Another benefit to having a jungling hero is the ability to gank without a call. Because they are always "missing," jungling heroes can often times surprise the enemy team and this can result in a very effective gank that could kill two people.
Importance of Communication
Dude, your microphone is muted.
This is a very important aspect to jungling; make sure that the players in the lane closest to you inform you of whether the heroes leave the lane because when you are alone in the jungle it is difficult escape a gank with no nearby tower.
Watching the Mini-Map
What are you starting at?
If your teammates in lane are not the type to call missing, then it becomes imperative for you to watch the mini-map yourself to make sure no one is coming after you. This is a difficult task while paying attention to jungling but after a while you will start to learn that it is your best defense mechanism, because pub players rarely call missing.
Microing Your Units
Prerequisite: Uber Micro.
This applies to heroes such as Tempest and Ophelia who are presumably controlling more than one unit. The key to jungling is to make sure that your creeps do not die when there are other creeps you are controlling which have full health. Particularly in the case of Tempest, you must learn to move away a unit if it is getting focus fired and try to spread out the damage as much as possible so that your creeps duplicate at least once. This, as with anything, comes with practice, but learning how to micro the creeps enables you to jungle more effectively and kill neutral camps you would not have been able to other wise.
Dealing with Disabled Spawns
Something must have scared them away.
Occasionally you might notice that a neutral camp isn't spawning. This is a clear sign that someone is countering your jungle behaviors. Any kind of ward placed very close to where the neutrals spawn will disable the spawn. The most likely culprits are Scout's Electric Eye or Keeper of the Forest's Tree Sight skills.
Scout's Electric Eye can be spotted by standing where the creeps normally would. This normally puts you close enough for the Electric Eye to become visible, a drawback to that particular skill, allowing you to destroy it. The cooldown for this skill however is only 30 seconds, so even if you destroy the Eye, chances are he will just put up another one shortly after. If you really feel that you need that spawn camp you can try to destroy the Eye about 10 seconds before the minute mark. That way you can hopefully run far enough away for the neutrals to spawn before Scout puts up another Electric Eye.
Keeper of the Forests Tree Sight can be a little harder to find. Look for a green eye above the trees, which can be difficult because you cannot see past the first row of trees. If you can find the eye, it's a simple matter of destroying the tree it is floating above. Keeper of the Forest can't put these eyes up more than once every 4-5 minutes early game, so if you find the eye you won't have to deal with another for quite a while.
If there is no Scout or Keeper of the Forest in the game what you're most likely dealing with are purchased wards. Combating this annoyance will cost you more money than you should be spending just to keep farming creeps. You're best course of action may sometimes be leaving the jungle, and laning like any other hero would. If you decide to remove Wards of Sight, that are blocking your creep spawns, you will need Wards of Revelations and a help from your Flying Courier to help you find wards that are surrounded by trees.
To remove Wards of Sight you will usually need to use your Flying Courier.