If you're jungle and 2 or 3 lanes are being pushed, what do you do?

You help what ever lane is WINNING for your team. It is better to have 2 people snowball, than to have an entire team go even or lose.

Example: you have a talon mid vs a zed, talon has a slight CS adv. vs their zed, score is 0-0-0 between them, then you look bot lane and your ADC is down 40 CS. Do you really think ganking bot will really accomplish much? Chances are their bot lane could 2v3 you guys. So gank mid, get your talon snowballing, and then he can help do your job roaming the map.

Just an example but i think you get the idea.

You go bot

Bot is (almost) always the right answer

If they're both at 10% HP and need to back, you make sure you're there when they return

Nobody fucking cares about top, they teleport out of there every chance they get for a reason

Which ever you feel will bring in positive results.

kill some more camps

You check if you see the enemy jungler, if you know his position the choice is much easier to make. You can either : farm, counter jungle, counter-gank or stealthy drag Obviously if you think bot is in danger of getting ganked but have no enemy jungler in sight, farm your bottom jungle so you can react faster. If you see your bottom lane getting gank and you're way too far to either save the tower/pick up kill/save them you can try to go help one of your laner to take a tower since they're already pushed according to the initial situation.

I find that decision making is the most important part of a jungler. Also knowing your jungler is a most, if you play yi/xin then counter-jungle or pushing is quite a good idea. Otherwise with Hecarim and your insane speed you might just get there in time to at least pick up a kill or stop the tower from falling.

TL:DR: Know what you can do (push/counter jungle/gank/drag/etc) and what you should do (all three lane are pushed enemy jungler gank top head for dragon or get his bottom buff).