Champion knowledge is a big one. If you know what the enemy champion is capable of and what their weaknesses are, you should be able to farm and trade a lot easier and come out on top. So like knowing when and how far away they can go in for a trade, when their power spikes are, when they can play aggressively, etc. helps a lot.
Practice CSing. go into a custom game with no runes or masteries and just try to last hit with nothing but autos. Do it for 10 minutes then leave. Rinse and repeat. Try to get a better score than you did the last time. That way when you're in a game with runes and masteries, it's that much easier. Also try to practice farming under tower.
Have map awareness, and ward. As a jungler you should have an idea when you would normally go for a gank, so that should give you an idea when the enemy jungler might. Keep an eye on other lanes too in case another lane is SS, or if you're running TP, in case there's a good gank opportunity.
Practice wave control. Learn how to freeze a wave, how to shove a wave, how to bounce a wave, etc. And know when to back and when to roam so you don't lose CS.
Nothing really groundbreaking or new here that you couldn't find in a youtube video, but maybe it'll help someone.
[slayer-jinx-catface]
