It took me quite awhile to gain pebbles and BamBam's trust.I found this article earlier this evening.I have never had trouble with mine biting.I hope this helps.
Taming comes mostly through treats. When degu is afraid of your hands, give him some treat, first through wires and later you can open the door so the contact with your hand is closer. And yet later you can hold the treat, not let the degu take it, so that he must chew every piece from your hand. Just don't give treats to degu too often so that he stayed healthy. Sometimes it don't have to be a treat - just before feeding give him a piece of his normal food, he'll take it rather from your hand thatn from food bowl.
Except treats, you will probably want to take degu out of his cage. But don't grab him by force. This is very frequent mistake. All degus are afraid if you try to grab them like hamsters or other pets. Degus are not lap pets, they would think you could be some predator if you take them from back and they can't see that it's you. Then they might become frightened yet more than before. The right thing is to place your hands and wait till degu will come to them.
While you play with your degu, speak to him. He'll remember your voice and when he gets used to it your voice will calm him down, he'll recognize you or even come when you call him. If you often say his name he'll remember this sound and he'll know that you speak to him when you say it.
Some degus can also bite even it's not very often. Mostly he is just defending from some bad experience in the future. Behave the same way to this degu, just be careful not to leave your finger before him too long - he won't try to find your fingers, he would bite you only if they are neat his mouth. If you be patient and he'll recognize you are nice to him and don't harm him (and give treats to him), he should stop biting. I found the info here.