Its all about gaining an advantage and consolidating it by doing the right things. Pushing when its the right time, backing off when you dont see the enemy team. Buying that extra ward. Going for the smart targets. Being positive for your teammates and ping a lot to show that you are there and willing to help. As a jungler, you want to focus on the lane that has the most chances of getting your team ahead, then proceed to help the lane that is behind only when you gained an advantage somewhere else... UNLESS this toplane
who fed 5 kills to
abandoned lane and the gator starts roaming or is getting the inner turret before 15 mins. Also mind that sometimes you cannot carry hard, but you can help your team achieve victory anyhow.
In my own experience, making plays to get that first couple kills is all it takes in early game. Then you need to think about what you need to do to enter snowball mode and denying comebacks to the enemy team. If you get a couple kills early but draw too much aggro and the enemy team shuts you down, then you made a mistake and you need to think about what events prevented you from getting more feed at this point. Another thing that you have to keep in mind is... who in your team is not doing their job and what can you do to prevent that from putting your team behind. Most often times you can 1- buy wards that your support isnt putting down (good return on investment when 1 ward can give you 1 kill right?) and 2- using the "bad player" in your team as bait.
Also, it all depends on what you mean by "carrying". Often my team will say to that 0/1/30
that he carried the team (madlife!!!). Or that
who was so good at calling shots that coordinated the team well (push this lane then ward that and group there) and got +4 teamwork at endgame. You can carry games by killing everyone, by making decisive plays, or by calling shots that will help your team achieve victory right? Sorry if that sounds like stuff you all know but imho thats what it is.