As a jungle main, yes, jungling is difficult to get into. It's very different from laning, and you have to know your limits. I suggest practicing in custom games first; get the clearing down before you try to add ganking to the equation.
Right now a lot of junglers are fairly weak and have some trouble clearing the jungle the first time. Unlike before the changes, you can't clear your entire jungle and still gank. Keeping up in level with laners is difficult or impossible, making ganks risky unless you know when and how to go in. So it's tough.
Especially coming into the new jungle as a new jungler.
I recommend Warrior over Devourer in general, unless you feel like farming the jungle more than ganking, because generally in a gank you burn all your skills on a retreating enemy, rather than sit there autoattacking them. There are exceptions, like Warwick and Shyvana, but that's my stance on it.
Warding is important too; warding your jungle and the river will result in nasty surprised for enemy junglers, because they don't get a jump on you, and your team will often respond to seeing the enemy in your jungle, because the small paths often mean free kills on a jungler caught out. Similarly, you don't want to be caught out in the enemy jungle, so make sure to either get Raptors buff before going in, or save a flash or similar skill.
When you gank, unless you're tanky and the enemy is low, wait until they're pushed halfway or more down the lane, and hope they haven't warded. Usually pinging your team will make them back off and let the enemy push a little bit so you can gank. Holding lanes is a good way to supplement jungle experience and gold, because you level slower in the jungle than in lane, and don't be afraid to tax mid or top a minion or two after a gank.
And as for taking Dragon, wait until your bot lane pushes to tower, or gank it if needed, before going to dragon. Make sure you can and do secure the crab; the movement speed will help leaving, both for laners to get back, and in case the enemy team is coming to check on/ward Dragon.
In general, as a jungler you have a lot of objectives and options of what to do, and it's often difficult to make a decision on what to do, so that's where the trouble comes in for a new jungler; a veteran jungler can make those decisions more efficiently and to a greater gain. For now you have to slog through figuring it out the hard way.