Practice, practice, practice.
Practice is key to improving your dice stacking game. The more you practice, the better you'll become. This should be obvious, but it's something that bears repeating. When you start practicing, improve your skills by doing so frequently: try to practice at least three times a week for twenty minutes each time.
Practicing in different environments helps you develop patience and focus—traits that will bring great benefit to your game. Try practicing outside in your backyard or in the park across from your house for variety's sake. Practice with different people too: solo practice is fine, but try practicing with others as well as a way of sharpening your interpersonal skills and engaging with the community surrounding dice stacking.