The strongest junglers in the current meta are (arguably):
Lee Sin,
Vi,
Wukong,
Pantheon,
Evelynn,
Elise,
Kha'Zix and
Olaf. If you like playing one of these champions, chances are it's going to be a bit easier to be strong in a lot of your games. That said, they're not necessarily the easiest champions to learn and you might have better success with a simpler jungler.
For learning jungling I recommend
Nunu & Willump (if you're pre-30 and/or want to be really supportive and roam a lot),
Nocturne (if you like farming a bit more and you want to learn how to manage your time well in all aspects of jungling),
Xin Zhao/
Jarvan IV (if you want really simple and powerful ganking junglers) or
Amumu (if you want to farm a lot and transition into a tanky initiator for team fights).
The standard jungle route is to start at one of your buffs (a lot of people start at the buff nearest to their bot lane so the adc and support can help you with it),
Smite it, clear wolves or wraiths (most junglers do wolves), then clear the other buff with
Smite, then gank or something. You don't want to do the wight camp (big solitary wraith) too early because it hurts a lot, so make sure you're at least level 3 or 4 before you kill that one.
Time management isn't so easy to explain because it's one of the most important and difficult skills for junglers. Depending on the champion you're playing, you're going to spend a certain amount of your time clearing camps, a certain amount of time roaming the map and a certain amount of time trying to gank lanes. Your job is to get as many successful ganks off as your team needs without falling behind in level. Try to execute most of your ganks within 10 seconds of you arriving at the lane and waiting in the fog of war. You don't want to be sitting in a bush for two minutes while the other jungler is farming just to get a gank off, even if it works. When farming the jungle, try not to walk past empty jungle camps (that you've cleared already) on your way to farm another camp. If you just finished wraiths and wolves haven't respawned yet, don't walk all the way over to wight, just do golems or gank mid or something while the camps respawn.
For just about every jungler you should buy your jungle item that builds out of
Spirit Stone before anything else (except
Boots) and try to consume your conservation stacks before they cap at 80. If you have a
Spirit of the Ancient Golem and the stacks hit 80, you're wasting potential gold that you could cash in on at the next camp. As long as the stacks are rising, you basically have a source of gold generation that you just have to cash in on every once in a while.
Itemization totally depends on the champion. A good olaf build is something like this:
, but you might have to change it depending on the enemy damage threats and if you're ahead or behind. If you're behind as a jungler, usually you'll want to get really efficient defensive items like
Randuin's Omen and
Locket of the Iron Solari (I hate locket but at least it's cheap). If you're ahead, you can afford to build more aggressively with stuff like
Sunfire Aegis,
Spirit of the Elder Lizard and
The Brutalizer, depending on the champion you're playing.
Last few general tips: Gank lanes that give you the best chance of a kill or at least blowing defensive summoner spells. This usually means ganking a lane in which your ally is ahead of the opponent, or ganking champions that have few escapes or are pushed up to your tower.
Try to keep track of where enemies are warding, look at your opponents' behaviour to tell if they know you're waiting to gank them, and place some wards of your own to protect your teammates and keep track of the enemy jungler. Being in the right place at the right time is how you can snowball as a jungler, and having vision of the map helps with that a lot.
Control dragon by keeping track of when it respawns (6 minutes after it dies), gain vision control of that area with wards, pink wards and
Sweeping Lenses, then group your team to dragon and kill it whenever it's up. Dragon is worth a ton of gold for your team, equivalent to a tower or 2-3 kills, so don't let it sit there for a long time or allow the enemy team to kill it for free. Baron is important too, but it's much more likely that you can win a game without killing baron than you can win a game without ever killing dragon.
If you have more questions you're probably going to have to pick a specific champion. If you don't want to listen to me blabber on anymore, find a champion that seems interesting and go look up some guides for that champion! See what other people are doing and what works in different levels of play. Check out probuilds.net to see what some high-ranked players are building for their runes, masteries, summoner spells and items.
Hope my wall of text was somewhat helpful. It might be worth reading a jungle guide, even if you don't play the champion, just to get some more general advice that could apply to whatever jungler you might be playing. I have a Nocturne guide with some good information in it but I'm sure other jungle guide authors have some helpful advice too.
EDIT: If you have some questions that require a higher level of jungle play than platinum, you might want to contact h4xdefender or C4 Lasty, they're both really good diamond junglers on the site.








For learning jungling I recommend





The standard jungle route is to start at one of your buffs (a lot of people start at the buff nearest to their bot lane so the adc and support can help you with it),


Time management isn't so easy to explain because it's one of the most important and difficult skills for junglers. Depending on the champion you're playing, you're going to spend a certain amount of your time clearing camps, a certain amount of time roaming the map and a certain amount of time trying to gank lanes. Your job is to get as many successful ganks off as your team needs without falling behind in level. Try to execute most of your ganks within 10 seconds of you arriving at the lane and waiting in the fog of war. You don't want to be sitting in a bush for two minutes while the other jungler is farming just to get a gank off, even if it works. When farming the jungle, try not to walk past empty jungle camps (that you've cleared already) on your way to farm another camp. If you just finished wraiths and wolves haven't respawned yet, don't walk all the way over to wight, just do golems or gank mid or something while the camps respawn.
For just about every jungler you should buy your jungle item that builds out of



Itemization totally depends on the champion. A good olaf build is something like this:











Last few general tips: Gank lanes that give you the best chance of a kill or at least blowing defensive summoner spells. This usually means ganking a lane in which your ally is ahead of the opponent, or ganking champions that have few escapes or are pushed up to your tower.
Try to keep track of where enemies are warding, look at your opponents' behaviour to tell if they know you're waiting to gank them, and place some wards of your own to protect your teammates and keep track of the enemy jungler. Being in the right place at the right time is how you can snowball as a jungler, and having vision of the map helps with that a lot.
Control dragon by keeping track of when it respawns (6 minutes after it dies), gain vision control of that area with wards, pink wards and

If you have more questions you're probably going to have to pick a specific champion. If you don't want to listen to me blabber on anymore, find a champion that seems interesting and go look up some guides for that champion! See what other people are doing and what works in different levels of play. Check out probuilds.net to see what some high-ranked players are building for their runes, masteries, summoner spells and items.
Hope my wall of text was somewhat helpful. It might be worth reading a jungle guide, even if you don't play the champion, just to get some more general advice that could apply to whatever jungler you might be playing. I have a Nocturne guide with some good information in it but I'm sure other jungle guide authors have some helpful advice too.
EDIT: If you have some questions that require a higher level of jungle play than platinum, you might want to contact h4xdefender or C4 Lasty, they're both really good diamond junglers on the site.

Thanks to The_Nameless_Bard for the sig!
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I'm joining a couple pals and since they have no other spots needing filling, I'm opting to stand in as their jungler. I'm not great at it, as my few forays into the jungle have generally been awful which is pretty telltale, but I want to learn how to be better.
I have Olaf and Fiddles with whom I think I would enjoy jungling most, but I also wouldn't mind learning more about the jungle in general. Who's good in it, good strategies in it, optimal routes. Itemization and progress is my weakest point, I can usually set up a gank or two but then I just sort of fall behind because I have no idea how to jungle optimally.
I would love a mentor, but I would love any tips, tricks, general notions and the rest of it. Any help at all, really, is highly appreciated-- I want to be a solid jungler for my team so that I don't let them down.