While Chanel had created the LBD in the 1920s, it was not a wardrobe essential until Givenchy designed the dress worn by Audrey Hepburn in the opening of the film. It's a sleeveless sheath floor-length gown and was accessorised with strands of pearls draped around her neck, a tiara on top of her beehive hairdo and dark sunglasses with a design reminiscent of Ray Ban Wayfarers (tortoiseshell frame). Apparently, the sunglasses were Oliver Goldsmith's Manhattan. Don't forget the black opera gloves.
The most distinct part of the design was the cut-out on the back of the dress. The lower half of the dress in the movie was redesigned by Edith Head as it showed considerable amount of leg when Hepburn had it on. It is this gown that epitomised the LBD and it's a style that'll never go out.
Throughout the movie, Holly Golightly is seen in different LBDs. With just a change of accessories, it's possible to make a dress suitable for any occasion. Keep it minimal during the day and if you have to make it a statement, put on one statement piece and you're good to go. A lot of her statement pieces are very neutral. For night, just add more accessories to glam it up.
To channel your own Holly Golightly, you should pick out an LBD that flatters your body. A shapeless shift dress isn't going to flatter anyone but if you pick out the right details, that shift will look good. If you're an hourglass for example, you'd want to belt it so your curves aren't hidden by the shift. If you've got a small bust, a boat neck will do wonders. Maybe the shift dress isn't for you and you want something more daring with cut-outs? It really is up to you and what flatters you.
Most of Holly Golightly's wardrobe consists of neutrals. Very minimalist and chic.