Step One: Know your role. Understand the difference between Tanks, Fighters, Assassins, Marksmen, Mages, and Supports. Find which one fits your playstyle and learn the different champions for the desired role. Also recognize that this will influence other parts of this little guide (i.e. supports not CSing, feel free to respond with questions).
Step Two: Watch your minimap. Think of a League game like a car, the area around your character is the road, and the minimap is the rear view mirror. You'll near always have vision on your character's surroundings, but that won't give you all the information you need to safely make the trip to the enemy nexus. So, you should look at your minimap about once every 3-5 seconds (ESPECIALLY as a jungler). It'll give you information on whether or not it's safe to engage on an enemy laner, invade the enemy jungle, or go in on a 4v5.
Step Three: Learn to CS. If you learn to CS (unlike many people bronze to silver) you can gain a serious gold lead that can even be worth more then accidentally giving up a kill or two. For context, about 15 CS is worth a standard kill (unless assists are gotten, in which case it's nearer to 20). Plus, CSing will help keep you from playing to aggressive just try to get a lead, since you will have one anyways.
Step Four: Learn to play to your team composition. If you are playing jungle and have a Fiora Top, Zed Mid, and Jinx ADC, don't play Rengar. This should come with time (about a year to year and a half of playing for me personally)
Step Five: Here is the most secret tip for playing anytime after laning phase. You will win any game if you and your team do this. Ready? You sure? Don't get caught out. Not being caught out creates less outnumbered fights, which causes less gold leads for the enemy.
I believe that's the multitude of general tips I can give you without any specifics on your playstyle. I hope this helps, sorry if I was over/underestimating your experience/skill. Any more questions, respond and I'll try to help. Until then, see you on the rift! <3 [slayer-jinx-wink]