As a plat jungler, I hope I can offer some tips. Do not think this is the only way to play, but I find it works pretty well.
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Farm. First thing you need to do is farm, don't even look at lanes until you have all your abilities. I know some low level Lee sins can take advantage of bad laners pushing super early, but don't bother with that until you feel confident in what you are doing.
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Control dragon. take the scuttle, ward dragon, take it when you know the enemy jungler won't contest it. (always have smite up for dragon)
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Know when you can gank. Check the lane before going in, if your ally is super low on health or mana, they can't help you fight the enemy. If the enemy is super ahead, you probably can't fight them despite the 2v1, etc. Knowing when it is worth your time to try to gank makes a huge difference. If you don't think you can gank a lane, or help push a tower. Farm. Don't wander around, don't hang out beside a lane. Go back to your jungle and farm more.
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Don't counter jungle. I assume you aren't diamond, you admit to not really knowing what you are doing. So don't get all aggresive and challenge their jungler on their turf. There are times when you can counter jungler safely. Late game, with your team, or when the enemy jungler is dead. Besides those times, you are taking a risk to go into the enemy jungle. A stupid risk, sure, you might be able to take their wolves, who cares? If you kill them, great, but what if they kill you? Just don't do it, you'll be fine.
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Ganking. So you see an opportunity to gank, make it clear to your teammate you are coming. try to come in behind the enemy. (ex. through tri). Depending on what you play how you use abilities in the gank will vary, but for the most part, try to use all your abilities. Don't walk away as Amumu never having used your Q.
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Helping lanes. youcan assist lanes in a lot of ways other than ganks:
Covering a lane, prevent the enemy form pushing tower, that's it. Take the farm, don't fight the lane opponent, easy.
Pushing a tower, If a laner kills their opponent or forces them to back and you are nearby, you can go into the lane and push it with them to try to take the tower. Even if you don't quite get it before having to back off, this is super helpful for pressure. (the laner may complain about you stealing farm, try to avoid that while pushing the lane, explain it to them when you get the chance).
Counter-ganking, This is the most difficult thing to do as a jungler. Assuming you have wards, it is easier, you can see the jungler before they enter you ally's lane, go there, try to help. Without wards you need to predict where the enemy might be. This is essentially asking yourself where would you be if you were the enemy right now. You won't always be right, you can't always stop ganks and you might try to stop a gank and waste some time you could have use to farm, but it's okay.
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Baron, don't call it unless you have your team with you and the enemy doesn't. If some of them are dead, or bot lane. This gives you an opportunity. Make sure you smite Baron, don't make a habit of letting it get to 200 first, or smiting at 1200.
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Don't get mad at your laners. This is like when you learn how to drive and you realize how all pedestrians are trying to get hit. When you learn to jungle, you realize all laners are retarded. They are going to get killed by obvious ganks, they aren't going to ward. They aren't going to help with drag, they aren't going to want to take towers. You have to tolerate this, and play around it.
Those are some tips I could think of, if anyone really disagrees, or has anything to add feel free. I think that is pretty comprehensive, not exactly "basics" but, basic thought processes for myself as a jungler.
fully stacked
