Not anymore a jungle main but the jungle taught me some things:
1 - Always prefer ganking winning lanes: Those who win theyr lanes 1 vs 1 have proven to be able to stand theyr own against the opponent so they are more likely to win the gank;
2 - Prefer to gank carry champs: This should be obvious even though most people don't get this. No matter how fed, that blitzcrank mid won't carry the game, while that vayne bot or that jax top might be able to do something;
3 - Don't gank lanes that are too much behind: you will just die and give a triple/double;
4 - Always make your own calls: You are the jungler, it's your job to control drakes and barons so do it, Also laners can't make calls since, if they are in theyr comfort role, they probably almost never jungle;
5 - Instantly mute flaming lanes: they will never stop complaining they lost 2 vs 1 bot, against the supp, because "you didn't gank us" and it's just a pain to deaò with them;
6 - Try do deepward as much as you can: laners can't deepward most of the times so you gotta do it yourself, else you will never know the enemy jungler's location.
Obviously these aren't strict rules: if the losing lane i a hard carry bot-lan you can try to gank them, especially if they lost in a close fight.