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!