Step 1: Materials
A sanding device (this is a cheapo $20 bench grinder, it'd be much better to use this cool sanding station from Craftsman)
extension chord (for working outdoors)
fine point pen
Step 2: Safety warning
Step 3: Grind down the sides of the dowel
Start by sanding opposite sides of the dowel till you get a rounded squarish shape.
Then sand the corners down until you have something like an octagon shape.
Step 4: Cut the shape from the dowel
You may need to sand the cut edges a little more.
Step 5: Write in your favorite tropes
Step 6: Roll them and imagine the film
Make as many as you want and then roll them and see what interesting combinations occur.
You might want to categorize the dice into characters, scenarios, objects, events, etc. and maybe color code them accordingly.
The most surprising thing to me is how often the combinations remind me of a movie I've already seen! Probably because tvtropes.org is a registry for hollywood cliches, but still it's fun to read and see it all cleverly documented.
My favorite combination so far is: Dug too deep + Crystal Spires and Togas + Merchandise Driven + Moral Guardians + Zen Survivor + Visit By Divorced Dad