People have their favorite recipes. I prefer the old classic recipe.

Basic 3-2-1 mixture-
1 1/2 oz white (silver) tequila
1 oz triple sec
1/2 oz fresh lime juice.
Combine the ingredients with ice in the cocktail shaker. Strain into the rimmed glass.
Some prefer a 4-2-1 mix.

Rimming
I saw a bartender at the Warwick in Houston do it as follows.
Set the rim of the glass on a wet towel.
Set the rim of the glass on a tray with a layer of salt.
Remove and fill with the mix.

I have tried several methods and found the above rimming method to be fast. None of my attempts were ever perfect.
It has been a long time since I was in margarita country, and a long time since I mixed one.

This thread will bring back memories.