Just because you are using pre-mixed flavorings for your drinks does not mean that you have to stick to the standard directions of so much alcohol to so much mix and that's it. You can always add your own little twists to the easy no-fail drink mixes.
Stir together the basics. When figuring out how to make a margarita with flavor pre-mix, mix it as it states in the directions on the back of the bottle. Add the right amount of tequila (or a little more if you're daring) to the correct amount of the mixed flavoring. This varies from bottle to bottle so make sure to check the label for the right portioning.
Add some more booze. This is done in trial and error based on the flavoring that you are already working with. Keep it simple--adding some strawberry schnapps, for example, to a already strawberry flavored concoction or add a little banana liquor for a twist. Experiment with a few different flavorings to find one that suits your palette. The most common food flavor combinations (say, apple and cinnamon) tend to translate well into drink flavors.
Throw it on ice. When figuring out how to make a margarita with flavor pre-mix, a trick to make it taste like the real thing is to treat it as if you are making the real thing. Fill a shaker with ice and pour your mixture into it. Shake it up well (just like you would when mixing all of the individual ingredients together) and set it aside to pour it later.
Grab some fancy glasses. If doing the standard flavored margaritas, grab a few wide rimmed glasses and push them down into a salt covered plate to coat the rim. If you want to do other flavors, grab the glasses and skip to Step 5.
Cut up some fruit (depending on the flavoring you used) and put either in the drink or stick to the rim of the glasses.
Perform Steps 1 through 3 in section one.
Blend up some fresh cut-up fruit. Depending on your choice of flavorings (the pre-mixed as well as the extra booze), cut up and put some fresh fruit in the blender. Turn on and blend until smooth.
Throw in some ice cubes and blend until smooth. (Add some more booze if you wish, whether this be the tequila or flavored alcohol, like schnapps.)
Add your pre-mixed drink concoction from before (from the shaker) into the blender and continue blending until well mixed.
Pour the whole mixture into some fancy glasses and garnish. The finishing touch on a margarita with flavor pre-mix as a frozen drink is to take some more cut-up fruit and add to the rim of the glass and serve immediately.