Some things to keep in mind
When you run across a delicious drink at a bar or restaurant, the ingredients are usually listed on the menu. Most bartenders are also quite willing to tell you how to make a drink, so ask them about it.
While you can buy bottled mixes especially made for creating certain types of cocktails, (eg. Margarita mix and Collins mix) these are not as good as creating the drink with fresh ingredients. Bottled mix leaves an artificial aftertaste that can be unpleasant.
Keep vodka in the freezer for best results.
To salt the rim of a glass, rub a fresh cut wedge of lemon or lime around the rim. Keep a shallow tray about 1 cm (3/4 inch) deep with salt, and invert the glass and dip gently into the salt. Move the glass gently from side to side, but do not spin quickly or the salt will simply absorb the citrus and fall off the glass. Use rock salt for the absolute best in flavor.
Never underestimate the importance of appearance. While a lemon slice garnish may seem to be the least important part of a recipe, do not leave it out. The appearance of a cocktail is just as important as the taste.
Avoid using wooden toothpicks as they will splinter and leave wood "floaters" in the drinks. Use plastic toothpicks, or a nice specialty set of toothpicks. Extra long toothpicks are always appreciated so that the whole thing doesn't drown in the cocktail.
Always plan for what your guests will be drinking. Generally, if you make a drink once you'll have to make it again and again, as people will often just drink what they see others drinking (especially if it is a trendy or colorful cocktail).
You can never have enough ice.
A shaker is essential! Don't use improvised shakers.
If you spill down the side of the glass while making a cocktail, transfer the contents to a clean glass. Just wiping the glass off will leave an unpleasant sticky residue.
If your guests can see you while you mix their cocktails, make sure your mixing area is very clean. Mixing drinks in the middle of a giant kitchen mess reduces the appeal of the cocktail.
Check out substitution list for information about substituting alcohols in recipes.