Garnish if desired. The proportion of gin to vermouth determines the style of martini. An all-red vermouth martini is enjoyed by some but looked down upon by most. Also very good are orange bitters. This boils down to personal preference.
Olives can be enjoyable, but onions taste foul in a martini.
The finest garnish remains the lemon twist. Never mix garnishes unless you be brave and don't mind ruining a perfectly good drink. The whiskey sour is a drink enjoyed by both men and women. Particularly good is the amaretto sour. Variations are performed by modifying the ratio of whiskey to sour.