Cut off the ends of the lemon and then slice the fruit lengthways into 6 or 8 wedges, preferably with a slit in the middle so you can place the garnish on, not in, the glass. Wedges not only look nice but they're functional too: by squeezing the wedges, guests can easily add extra lemon to their drink without getting their hands covered in juice or pulp.
Lemon is also a great garnish for its natural properties concentrated specially in the peel:
Lemon Zest Twist
Cut a thin slice of lemon peel using a knife scrape off the pith; run the twist around the lip of the glass. Twist it over the drink to release the oils and drop it in. You may also flame the oils when they are squeezed out of the zest for getting more flavor and make it more attractive.