There is no secret. The edge is on the house.
I would invest my BTC in many of these Dice sites but the chance of them getting hacked is not worth the small gains.
And even when you get a small gain, how do you think these gambling sites get theyr income? Right, by letting people lose.
And even when they win something, big chance they will gamble the amount won. It is all about money and nothing is fair in this game.