I, being a former magician (the slight of hand kind, not the wizard kind), have particular spots on the table that I like to roll them and like setting them and picking them up in certain ways (so I can bounce them off of beer bottles, etc.) in an attempt to improve performance. Being a former magician, this doesn't work as often as I'd like so I only do it when I really need that roll.
To prevent me from weighting the dice, we use a Chessex dice block and randomly dole out the dice.
Do those count as strange rituals?
In my game, I would never let a former stage magician or sleight of hand guy roll their own dice. It's not that I don't trust someone like that it's just I don't trust someone like that...
Going off that, the people I've gamed with have lots of little traditions.
While we're on the subject, the groups I game with always play Ravenloft the same way, only DM rolls dice behind a DM's screen. Works of Cthulu too. Halloween gets fun....
In the groups I've gamed with, it's bad luck to roll on top of any kind of battle mat. Hex maps, square maps, doesn't matter.
We could be playing Cyberpunk 2020, which we always always always treat as, "Whatever you roll, happens..." (It's Cyberpunk) and if someone rolls on the battlemat we'll say, "Don't roll on the Mat! It's bad luck!"
One of my gaming buddies gave me a tradition of, if I can, I will buy a new set of dice for each character I play. It's their dice. The buddy that start the tradition actually refers to her dice by the character's name. "Come on Tanis!" *Rolls poorly* "Tanis is being stupid. Let's try Realtor."
If my character's dice start messing up, I might use another set if I feel I've "Miscast the role." I then scold my dice for not taking direction.
For the DFRPG I've broken this tradition because I have so many characters and because I ran first that I only really need one double sized set of Fate dice. But I also bought them from the Chessex booth at PAX so I consider them blessed by the Powers of Gaming That Be.
We also retire dice that tend to want to kill us. Too many ones, sorry little dice.
Our usual solution for retirement is to give the dice to someone else and 100% of the time, the dice will roll like god for their new owners. Traitors....
I also have the superstition that my dice need to have the failures rolled out of them so that karmically they will roll well. They start rolling 1's and 2's and 3's, the next one's going to be a 20. It doesn't always work....