Dragons are the most selfish and self-centered creatures on the entire earth, so among all the animals in the world, they are the hardest to train. Not only are they greedy, they are also vicious, which makes training a dragon a very difficult task. However, dragons will listen to you if in return they are given a treat or a gift. So, the only way to train them is by bribing them with things to make them to do things properly.
The first thing to do in the process of training a dragon is for the dragon to be able to listen to basic commands like: "Run!", "Jump!", and so on. The dragon may not even need bribes to complete these tasks. Then you have teach them how to do harder tasks like catching fish. This is when you will have to start bribing. If you get too fed up with this you can stop the training and just leave. But if your OK with having to bribe your dragon for him to do everything you tell him to, then you can go on. Anyway, then, you also need to train him to sniff for things. Dragons have to be good at sniffing because having a sniffer by your side could come in handy once in a while. Anyway, try to hide some precious things under a pot or something, or bury it, and tell the dragon to find it. Of course, the dragon might not be able to find the precious object since it is only his first time.
Finally, you have to train your dragon how to fight. Dragons, as I had said are vicious, and viciousness also can help you in dangerous circumstances. Probably, first, start off with something simple, an insect perhaps. After the dragon is good at catching flies you can move on to other things, like a rat. Once it has crossed that level, then, comes the finally part: fighting other dragons(the same size as your dragon). If he has gone through that level, there is still one more level, which is conquering and fighting big dragons. The only way a dragon as small as itself can defeat a big dragon is scurry around its body and make the dragon attack himself, or probably just do something to distract him like saying, "Bet you can't set fire to that tree," or maybe you can just use something like, "I'm very poisonous," When the dragon is fully grown, probably you can teach him how to FIGHT a big dragon.