Well, you make them in a blender...and you use crushed ice.
The way I do it is to use real limes...
1 part freshly squeezed lime juice (it must be fresh fresh fresh)
1 part tequila
1 part triple sec or couintreau or gran marnier
1/2 part water or water with just a splash of freshly squeezed orange juice
Shake it all together. (We prefer ours shaken and over rocks) with a slightly salted rim.
Salt the rim by dipping an edge into fresh lime juice then tapping in kosher salt. Knock off excess salt by tapping on glass as it's tipped, so excess can fall off.
We find by doing a 1:1:1:.5 proportion, the grand marnier we use, makes it sweet enough for our tastes. The little bit of water, helps to cut the overwhelming acid bite to mellow it. The little squeeze of oj adds a bit of sweet too.
If you want to blend it, leave out the water and instead place your liquid in the blender and add about 2/3 that same volume of ice...