This is going to be a general guide tackling the core concepts that you should take in mind when jungling.

I'll try and keep it short and to the point. If you want to skim it just read the bolded sections

There are three things that make jungling unique

Farming,

Ganking, and

Neutral Objectives

Here are some things to keep in mind:

Farming is the main source of income for junglers.

• try to keep jungling in a straight line (top to bot, bot to top). It'll reduce the amount of time a camp goes unfarmed.

• kite properly, in general you should take 2 hits then back off. This ensures that you always deal more damage compared to the monster. An exception to this is raptors which depends on the champion you play

• scuttle crabs give give a good amount of money

Ganking is the main way a jungler influences the map:

• Identify which lanes to gank before the game even starts (Does this lane have a lot of cc, is it worth trying to get this lane fed, does the enemy have mobility and flash)

• During game, you should pay attention to the state of the lanes (Is top pushing and can I dive, is botlane getting pushed in and do they have wards)

• Ask your lanes if the enemy has flash (This is VERY useful information)

• Failing a gank can put you in a massive disadvantage so try not to gank unless you have at least 70-100% certainty that it will work (your laners might hate you)

• Try not to gank if your entire jungle is up (Especially early game)

Neutral Objectives/dragons and barons:

• They're important but not as important as most think

• if you see the jungler top, try and do dragon, if you see them bot, try and do rift

• When deciding when to take baron make sure that you can get something out of it (will this baron close out the game, will this baron last until dragon, can this baron give us some breathing room when we're behind)

• Try not to take neutral objectives if your entire jungle is up (Especially early game)

If you're just starting out I recommend just focusing on one concept at a time. Play a game where you just want to farm a lot, a game where you want to gank a lot, a game where you want to take a lot of objectives.
It'll make it easier

THERE ARE EXCEPTIONS TO THESE (a LOT of them). But in general, try to follow these. Treat them more like guidelines.

Here are a few cool things you can do as a jungler.

It's not as important as the ones above but it's useful stuff

Skirmishing/Invading

• Do this to make the enemy jungles life a living hell if you're ahead. Take his camps, murder him in his own jungle, make it so he doesn't have fun. Takes some serious balls to do though.

Jungle Tracking

• If you know the enemy jungler started bot because his bot was leashing him, and you spot him at raptors with blue buff and 4 cs (press tab). You can infer that he only took his blue at bot side. If you're at bot side just invade and take his camps, and also warn top.

• This is basically just simple deduction using the enemy junglers cs (4 cs = 1 camp).