See also Dice control
"Praying to the Dice" is a concept which most Real Roleplayers have at least considered if not wholly believed. Where some would dredge up concepts like the "science" of statistics, people who know their math and strong believers in the religion of luck know better.
Basically, timing and luck.. a "mood" if you will, influences the outcome of dice. While this is usually considered a lighthearted joke people comment on, it's not exactly, shall we say, "not real". To some it's an intriguing tug on their intuition, to others it's as real a belief as is seen in spirit-worship. Let's just compare it to Animism (a belief in a spiritual presence even in objects).
So how does one do it? Well, if you're in a bad mood, feeling unlucky or are a jerk about having to roll, then the odds are you'll roll mediocre. If you're just laying back having fun with some pals, you'll probably roll reasonably usefully -- Good when you need to, bad when it doesn't matter. Some people can call what their dice roll when they need to. I myself have done this.. literally called a specific number when I've been really into a game, in character and emotionally-charged.
Some people have unusual practice when it comes to dice. Some only roll on certain surfaces, or treat dice which roll off of that surface as not counting. I myself reroll all dice if one falls off. Some will throw away the entire set if they lose one die. An unusual practice I've seen is that when a moment calls for one die to be rolled the person will call one die and roll two, taking the one they called. When rolling 2d10, I know people who will roll the die without calling and will take the leftmost die as the high number. Personally I hate this practice, but whatever.
Some people like older dice, some newer and shinier. Some GMs will have preferences. I myself do not accept dice without numbers or clear visibility.
Some keep new dice on their person for a long while, or keep them with older dice, before really using them. Some will sleep with their dice under their pillow for a while. Some people will never let another use their dice.
The opposite exists.. people who barely own dice, or forget them and just borrow away. I know people who own spare "loaner" dice just to hand out to others.
Many varieties of person exist, and treatment of dice can become quite unusual.