Establish a practicing area for the child that is secluded and private. A regular area for the kid to practice helps remove stalling and legitimate excuses for not practicing. Make sure the room is well lit, preferably with natural light, and large enough for the child to practice comfortably.
Remove as many distractions from the practice area as possible, such as distracting posters or clutter. It is also a good idea to remove any toys from the area so the child is not tempted to play with them. If there is a TV, stereo or other distracting noise nearby, turn it off so the child can practice in relative quiet.
Schedule regular practices times with the child so that he knows how long to practice. Regularly remind the child to practice when it is time, and be consistent so that a habit can be formed. Check in from time to time to see if the child is practicing, especially if the instrument is quiet.
Give the child incentives through promised rewards, such as snacks or access to games. Small rewards for good practice time should be coupled with long-term goals and prizes set out clearly in advance, such as a party for the child or some new toy.
Encourage the child when you hear progress over time, and foster an appreciation for music, even if it is not the same genre the child is practicing. Take the child to concerts if it is appealing, or encourage the child by finding a friend for the youth who also plays an instrument.
Practice with the child if you play an instrument. This is also a great way to simply spend time together. If you make it fun, the child is more likely to want to practice more often.