I wouldn't add simple syrup to a margarita, it sweetens the drink too much for my liking.
You might start with 2/2/1 tequila, triple sec, lime and vary the amounts till you find the ratio which you like the most.
Another mixutre you might like to experiment with is tequila, lime and agave syrup.
It seems there is no commonly agreed on ratio but the ingridiens are used at a lot of bars and the drink is typically called Tommy's margarita.
I like it best at a 6.5/2.5/1.5...