General Tips
The best way to learn how to play League of Legends is simply with time. The more one plays, the more one understands the inner workings of the game and general mechanics. However, there are a few things that you should be thinking about before and during the game that aren't always as apparent. Counter picking in champion select and understanding how to go about jungling when your entire team is winning are often subjects that aren't talked about. This is primarily because counter picking is a fairly advanced skill to understand completely and in most games all of your lanes will not be dominating. However, they are situations to consider and give thought to regardless of your skill level.
Champion Select
While you're in champion select still, you should consider your position in the pick order. Most junglers are not highly contested picks, and unless you know your team wants a specific jungler, try to see if you can swap with someone else. If you are last or near last to pick, it is much better overall for your team if those higher in the pick order picked your jungle for you, and then you would pick their role at the end. This helps to avoid the enemy team countering key roles, such as mid or top. Another strategy could be picking abnormal junglers, or those that could go to a variety of lanes. This adds to the mindgame of champion select, in the sense that you are trying to force the enemy to think you're going somewhere that you're actually not.
In-Game
As you're going about your first clear in the jungle, there is not much activity going on. This is a good time to access your lanes and try to see who will be in the most need of your help. After your first clear or your first back, either ask your team who thinks they will need an early gank, or try to determine for yourself and make plans accordingly. If every lane seems to be dominating in the early game, continue to power farm your own jungle. Aside from continued farming, you should simply just try to hover around where the enemy jungler is. For example, all of your lanes are winning and you see bot lane pushed to the enemy tower, in this case, it would be best to hover around bot side to be able to possibly engage in a counter gank.