Dice tend to accumulate positive and negative energy. Positive energy gives good rolls and negative energy gives bad rolls. Another key to good dice rolls is mental thought. The mind can generate powerful mental waves that can control the roll of the dice. The will of the roller is one of the best techniques for dice rolling.
Some suggestions are in conflict with other suggestions.
Choose the ones that work best for you and ignore the other ones. The first set of dice you purchase will be the most lucky no matter how old and decrepted they get. When purchasing a die, roll as many dice of that type as many times as possible. When purchasing a crystal die, try to get one with air bubbles in it. They work better.