Article in English: Eventually you will need to stop issuing treats for the behavior.  Do this gradually by offering treats only every other time he performs the “shake” command.  Substitute praise or other rewards, such as a walk or playtime, in place of treats.  Keep practicing until you are positive he will “shake” without a treat. You can try offering an empty hand, with no treat, when first starting this step. Once you feel that your dog has mastered the “shake” command, try introducing challenges for it.  Wait for a situation that usually bothers your dog, such as a visit to a busy place or someone coming to the door, and issue the command. The more situations you practice in, the better your dog will be able to perform this command. Follow the same order of training as you did with the first hand.  The main difference will be that you hold the treat in your opposite hand and only reward when your dog shakes with the desired paw. Try using a different command word.  If you used “Shake”, try using “Paw” for the opposite hand.

Summary in Vietnamese:
Bắt đầu bỏ đồ ăn đi. Nâng cao tính thử thách. Hãy bắt tay bằng tay còn lại.