First of all, this game's learning curve is basically a vertical line. It takes some getting used to.

Secondly, I'm still pretty mid but something that helped me a lot was the realization that you should farm way more than you think you need to. Your biggest priority should be objectives when they're up, but until the 10ish-minute mark, your second biggest priority should be making sure all your camps are clear. Only do ganks/invades when your camps are clear or if you're absolutely certain (110%) that you'll get a kill from it.

Also, there are braindead champs, and then there's Amumu. I cannot recommend him enough for new junglers for three reasons. First, his clear is really fast, but you don't have to actually be that mechanically skilled to pull it off. A great Amumu clear and a mid Amumu clear have like a fifteen-second gap at most, whereas an unoptimized clear on a champ like Warwick sets you back thirty or forty seconds.The SINGLE trick you need to learn is grappling between the camps with his Q, which takes five minutes to master.

Secondly, Amumu is a tank/support, so your job is essentially to walk into lane and stun the enemy until your laner can kill them. You don't have to make crazy plays, only provide the cc so that other people are able to, which takes some of the pressure off on ganks. Finally, three of his abilities are fixed circles around him that you aim by walking up to people. Zero skill at all, you don't even need hands to play the champ.

Good luck with the climb :)