Trying to get into jungling, but how do I gank?

Yeah, on your first back, swap out your yellow trinket with a red trinket. Then, try to use it on bushes when you get into ganks. When you go towards the lane, if they back off, just leave. If you think they know you're there, leave. Not worth wasting your time. If you're in bush, ready to gank, try to wait until they blow any cc/dashes as poke(assuming they're pushing against your laner) or at least wait until they go up to grab a cs. That's the best way. Watch your minions health, you don't want to be running into lane as they're getting that cs(you can, but not quite as effective), you want to be running in when they're going towards that creep to kill it(anticipate it, almost, but wait until they start moving to it).

The above is assuming the enemy laner is pushing against your laner. If it's going towards the other way(but not under tower) you can try going up the lane(from your side of map) into the bushes, and wait until you see an opening(I.E. blown engage/disengage). This is most difficult because generally waiting just for them to go for a cs isn't always enough.

TL;DR Wait until the enemy laner goes for a cs.

Smite chickens. Try to make sure they don't see you coming. Try to come from an angle that cuts off their escape route, or try to delay them with cc (Diana has some) so your laner can get some damage in.

Any time your opponents push past the halfway point of the lane it opens them up for a gank.

As you are jungling you should primarily be watching the minimap and the other lanes, not your character. What you are looking for is movements by the enemy team that show you where they are placing their wards. Keep track of ward timers and avoid those areas of the map until the wards time out. Not getting spotted by the enemy team is just as important as ganking. You want the enemy team to fear that you could gank any lane at any moment.

For ganks to be most effective you need to chain CC together. Chilling smite really helps junglers who don't have a lot of CC in their kit.

Always pay attention to your level compared to the lanes. You should be equal in level to your ADC. If you fall behind in levels your ganks will become much less effective.

I cover ganking a lot in my videos. https://www.youtube.com/channel/UC2EZm50wNGmfJal7IHM_b8Q

Pretty much the same way you would gank as a support.

If you get a summoner blown, it's an effective gank.

Like a mutha effin train - CHOO CHOOO!

You just have to wait for a good opening on the opponent that you are going in on. If you're a jungler with CC then it's usually pretty easy to just wait out that right moment, go-in and then help the lane.

There's good advice here. Additionally, if you're ganking a solo lane it's a good idea to wait for the target to blow an important cooldown. For example, if you're ganking a Riven, try to wait for her to use her Q charges before going in, that way she'll have a really hard time escaping from you.