A good waistcoat can instantly give any standard suit a boost, as well as making your stomach look more trim in the process. Opt for double-breasted styles for a traditional tailored look and always match the waistcoat colour to your suit, unless you plan on wearing the waistcoat without the suit jacket.
For a tailored evening look, wear a grey waistcoat over a white shirt and pair with slim fit jeans. Complete the outfit with tan leather brogues or chukka boots.