Hey guys I'm Bronze II this season and I've been playing League since about half way through Season 4 and have been a Jungle main since Late Season 4 and one of my friends wanted some advice with jungle and although I'm bronze and so most people will probably be better than me I decided that I might as well make a guide for anyone who needs it.
Ganking is in my opinion one of the harder parts of being a Jungler when you first start. After about a year of Jungling, I've made a checklist of things which you should look for before ganking
In my opinion the first thing you should look at to see if you can gank a lane is if it is in a good position to be ganked, if all the other criteria is fulfilled, but you're friendly laner has pushed the enemy up to their turret, ganking is probably going to get you killed unless you can pull off some serious insec plays. On the other hand if the enemy laner is at your laners tower the only ways they can retreat are through your tower or into you if you gank.
The next thing you should look for when ganking a lane is how far behind your lanes are, usually if a lane is behind and the lane is in a good position to be ganked, this is the lane you should gank. However at lower MMR sometimes a lane will feed to the point where if you ganked that lane you would just be feeding another kill, however this could have just been me first getting into jungling and being bad. note thaat this is not the most important thing, often in low MMR a lane will be behind and crying out for ganks but always be pushed forward so it is very hard to gank them succesfully.
Whichever lane you are closest too. This is pretty straight forward, bot and top are both in a good position to be ganked, you're closer to top, gank top.
The third thing you should consider when ganking a lane is whether or not you can make an enemy lane tilt. This in my mind is one of the joys of jungling, if after ganking a lane 2-3 times an enemy gets annoyed in all chat, that is when you know that you want to camp that guys lane if you can. As a jungler making enemies tilt is definitely a big thing that you have, you gank the enemy, they die, they get mad, they play worse, you gank again, they die again, they get even more mad, etc. One thing that I find accelerates the tilt is saying something like "ez" or doing a smiley face in all chat after a successful gank.
Finally, gank the dude who's complaining. Mostly to stop him complaining. I did to many terrible ganks when I was a complete noob just because a laner complained, no matter what even if you are threatened to be reported, make sure the previous things are true with the lane first (note that you should always gank this lane if you have already helped other lanes and in some cases it is better to do this before making someone tilt)
eventually all of this should become subconcsious