Tip 1: Make a habit of keeping those main mixers you use the most.  Only purchase additional mixers and garnishes when you are feeling adventurous with your cocktail recipes.

Tip 2:  Try to stay away from bottled mixers (i.e. margarita mixes, bloody mary mixes, etc).  Instead use fresh ingredients as much possible.  It makes a world of difference in the quality and taste of the cocktail.

Tip 3: Prep garnishes ahead of time for large parties.  You don't want to stall the fun!