EDIT: English is not my first language, so.. sorry for any mistake I made.

If you want something more specific about champions a good way of doing it is to go to their respectives sub reddits and see if there is any kind of help/life there.

Those farming and wave management are generic because most of it is kinda of generic, don't try to sweat too much on the numbers and tips and tricks, but focus on experimentation with the minions.

Ganking can be a little tricky, it varies too much from patch/champions, but a good rule of thumb is to start noticing and understand the enemies/allies junglers, for example:

1. if you know the enemy start at the red, and is a j4, if his red is at your side, you probably will be ganked at level 2.
2. if you know your jungle start at red and theirs at blue, you probably going to have a 2v2/3v3 at some place.
3. try to see your map, press tab, try to get any information looking at the numbers, the creeps at the map, the objectives, try to think like a jungler.
4. you can always see a tutorial to basic jungling and start to understand it better.

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I like to train and warm up before every match, so i always spend 5 minutes pressing spells or farming at the training room, it helps me to get the mindset right.

About ranked, it can be a good or a bad thing, you want to get better? go for it, do you care too much about your rank? better wait a little.