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DJ Semper's Guide To Jungling Part I
Probably the most disputed role in the game, the jungler has the power to make or break a game simply by recognizing the dangers the enemy team poses to his own team and by augmenting the strengths of his own team by ganking lanes that are more advantageous and taking the global dragon buffs and scuttles.
Ganks
What are advantageous ganks? Ganks where the enemy champion has limited escapes, does not counter either of your jungle nor the laner(s), and is in a position to allow you to enter lane cutting off escape avenues while allowing you to unload a large amount of dmg in a short time. A great gank should take place over moments. It should never require diving under turret or take long enough to risk the assistance of other enemy champions coming in should your loss of health in the gank bring you dangerously low.
Krugs.
Save a smite for these guys and take the bottom krug after you take blue the first time. It gives you a chance to regain some of your hp, get some addtl coin, and provide a great path for you if you need to get to your jungle quick since it gives you a movement speed buff for you or your roaming lanes when they move through it. In addition to all these great bonuses, your bot lane gets a free river ward that can't be blinded with a sweeper or taken out prematurely saving them from possible ganks. Right now, bot lane is a major focus for team ganks and one simple move can really give you a huge advantage. It will also let you know if the enemy team is trying to take dragon and give you vision on one pulled out so you can time a steal or team fight to your best advantage.
Ganking versus holding lane.
One huge mistake I see all the time is jungles going to help their lane by ganking when the enemy has a hp and mp advantage just because the enemy is heavily pushed in. If your team is near death, a 2 for 2 is a terrible idea. Let your team go b and farm minions. If you can, you freeze the lane at the turret preventing the enemy from building waves and denying them xp and easy farm. Give your team time to get at least halfway back up the lane and then hop back in your jungle. Why is a 2 for 2 a bad idea? Well, if they're already pressing you, you're not gaining any advantage at all by letting them have 2 kills. Plus, they get to split two kills of xp across two people while you have to share 2 kills across three people. On top of that, often the adc is lucky to get one of the two kills in a low hp gank because the jungle has more hp and mana and is therefore far more aggressive. Sure, a fed jungle can be nice, but not at the price of feeding the enemy bot lane and snuffing your own. Every time you move weight on the scale to one side, you take that much from the other. So if you bot lane A gains 300, essentially, bot lane A gained 150 and bot lane B lost 150. That's the way to view it to gather the gist of the difference in lane advantage.
Ganking suffering lanes.
It happens all of the time. Your top laner or mid laner got counter picked and they keep getting destroyed in their lane. It's four minutes in and their already down one or two deaths and they have 12 minions versus the enemies 50. You want to go and gank, but the other guy already does huge dmg and is 2 levels up. You think the two of you should have the advantage but in reality, this early, you just don't versus a fed champ. Not to mention, there's a good chance that the enemy jungler is lurking nearby because now your weak laner is basically a demoralized super minion who's hopefully going to spread his cancer to the rest of your team like the plague. So, if you go in, you're already risking losing to the other guy. He's definitely going to focus the suffering laner first and then, possibly kill you too and you definitely do not want to let him get two kills. And there's the additional risk of the enemy jungler and/or mid coming up and helping prevent you from shutting him down and putting the lane back in order.
Unless you counter the enemy champion and have enough cc to give you a great advantage as a duo, you need to convince your laner to back off and farm under turret. Then, focus on ganking one of your lanes that's doing really well. This might even mean focusing on helping them take a turret mid lane or bot lane. Top lane is super underestimated in it's relevance not to mention it's free global gold for your team every time you take a turret. So if you take mid or bot, don't auto rotate mid, shut down their top NOW and take that turret before the rest of their team can realize what's going on and react. If you weaken the outsides of their team, your minion waves can create more pressure to their second tier turrets drawing their teams away for easier pushes mid, jungle stealing, or even the occasional teleport to steal a 2nd tier turret. All because you didn't gank a weak laner. Remember, if they're losing and they're not being ganked and they're not countered, they're not mechanically or strategically sound. You're taking a risk ganking for that lane unless the opponent is at a position of strong disadvantage.
Ganking for a dominating laner.
There is nothing like being 3-0-0 in your lane and destroying the guy on the other side but he keeps pushing out. Suddenly, out of nowhere, your jungle comes in and steals the kill. You just lost half the kill gold, half the xp and your jungle is benefiting from work he's not doing while another lane could really use him or the jungle's still up. Don't be that jungler. If you want an assist, that's not so bad, but unless you're already way behind on your gold and xp because of counter jungling punishing you, you shouldn't be behind or need to steal from your team. Go up, get a hit, pass on some assistance, and let your laner get his kill. That 4-0-0 top lane is a greater advt and far more willing to help late game than the 2-0-2 top laner who keeps losing kills to a jungle who comes in and cleans up his work.