Anybody have any good jungle tips for a returning player?

I stopped playing League of Legends about 2 years ago, and now I'm back in action, but a lot of things have changed. I think I understand what I'm supposed to do in most of the roles again, but jungle is still giving me grief. For instance, I love playing as Hecarim, but I didn't do great. I mean, I wasn't absolutely dreadful, but I wasn't an amazing jungler by any means. I'm asking because I see other junglers do pretty darn well, like an opposing Hecarim who destroyed everyone, but I don't get what the difference was.

Now, I am basing this off of one game as a jungler, but I still need the help.