Hmmm trying to think of advice that you already don't know, but in general, objective control is extremely important. If you're able to keep tabs on dragon, herald, baron and when you can take towers, your team will be so much better off.
This definitely varies from game to game (as it depends on champs and players), but I find it's better to focus on lanes that aren't behind, and encouraging any behind laners to play safe and wait for the opportunity to get ahead with your help.
The example that comes to mind is when you're barely level 5, and your top laner is level 5 against a level 7 champ who could easily 2v1. In most cases, ganking that lane will net nothing, will lower the actual help you give elsewhere, and will give the enemy team better objective control.
Between farming and ganking, a mix of both is the best. If you want to gank bot in a few minutes, plan to clear your bot jungle, or have it up in time for after your gank. The best part about farming is that in most circumstances, it's risk free as you are guaranteed gold and experience.
The more assured a successful gank the better. If your laner is pushing up, you probably can't do much, so it's not a bad idea to ask them to freeze the lane or let the enemy push while you get a jungle camp in the meantime.
I like to invade when I know where the enemy jungler and team is, and try to make sure that if things go bad, my team is in a position to help me out.
Other than that, game attitude is important. Encourage your team, don't get angry with them, and overall just adopt a positive attitude.