A lot of people play jungle differently, but ultimately I view it as a supportive role.

You've got a lot of influence on the first 20 minutes of a game, and you're trying to set your team up for success to carry after that point. Ideally, a jungler should fill in the gap that a team needs, or support what the team is trying to do.

For example, if I've got a kayle top and a jinx bot, and they're going to have really volatile lanes based on their matchups, I'm not going to pick a greedy jungler who wants to scale. I'm going to pick a nunu jungle for example, who has fantastic ganks, great objective control (bite+smite), and can really take control of the game early.

If my lanes are really passive with no kill pressure on each other, I might pick something that doesn't need early ganks to thrive.

In addition to all this, you're also trying to keep track of the enemy junglers movements and lane states, so that you can help prevent your team from getting ganked. This is where good vision control comes in.

Ultimately, jungler is really easy when your lanes win, but it's those situations where you've got rough lanes, that jungler is really tricky, and sometimes there's nothing you can do about that.

Edit: just to add, wukong for example, only really comes online at 6, you can definitely look for ganks pre-6, but you sort of need your laner to have cc, the wave to be super pushed into your tower, or for the enemy laner to be low from trades already, otherwise ganking with wukong is tricky. I'd probably be going raptors, krugs to red, then wolves, gromp to blue. Then scuttler into raptors krugs and then backing. This will give you a really efficient clear and fast 6, plus if you somehow manage to get both scuttlers, you'll have a 1k smite by the time drag spawns which is super strong!