The "secret ingredient" in the original Mai Tai cocktail is the orgeat. Its flavor should be present in the Mai Tai, but not overly so that it takes away from the subtle balance of each sip.
If you have trouble finding orgeat in your area, you should be able to find clear almond syrup anywhere that they sell coffee syrups and flavorings. It'll work well as a substitute - the only real difference between orgeat and almond syrup is that orgeat is usually slightly cloudy, and usually has a little bit of orange flower water added to it.
1 ounce light rum
1 ounce gold rum
1/2 ounce orange curaco
1/2 ounce orgeat (almond syrup)
1/2 ounce fresh lime juice
1 ounce dark rum (optional)
Shake all your ingredients, exclusing the dark rum, with ice in a cocktail shaker. Strain everything into an old fashioned glass, then top with the dark rum.
Garnish with a maraschino cherry, and a sprig of mint. Serve with short straws if desired.