Output
1950's retro design styles can be used wherever a nostalgic, mid 20th century content is present. The whimsical, fun, lighthearted and playful "pop culture look" of the era can also be applied to basically any content where this lighthearted feeling is appropriate. In these cases the product that the design is created for need not necessarily be founded in the era, i.e. the 1950's. Highly contemporary products and concepts that call for a playful, humorous and/or illustrative approach from food to fashion will benefit from having this style applied. Candy, soft drinks, retro fashion, rock 'n roll events, nostalgia and music, youth oriented products of many descriptions can be designed with retro concepts.

On the other hand the highly sophisticated look of mid 20th century modernist design is essentially timeless: Alexei Brordovich's page spreads or Bradbury Thompson's design investigations retain their original impact as much today as on the day that they were published. This style can be applied to any subject matter where refinement and sophistication are called for: Corporate Identities and publications of upmarket businesses, restaurants, haute couture fashion, architecture, interior design firms are those that immediately spring to mind. Bear in mind that the fashion magazine concepts, from the hard serif typefaces to the layouts sets 50 years ago by the likes of Cipe Pineles and Alexei Brodovich are still implemented in todays upmarket fashion magazines, from Vogue to Harper's with practically no significant changes.

Thus we can head in two main directions where design based on mid-century concepts is applicable: The colourful, fun shaped, illustration and clipart oriented "pop" style of the 1950's or the sophisticated, upmarket modernistic look.

Mid Century Modernist
Keywords
Typography: Hard serif fonts such as Bodoni and Modern. Also era referenced script and brush script fonts. Here I will advise caution: There are some very ugly brush script fonts around, some even very well known and widespread. You will have to use your discretion and taste but when in doubt err on the side of caution. The same can be said for the following: Plenty of script fonts have a stylistic reference that is completely different from retro design in that the reference is essentially Baroque. Englische Schreibschrift constitutes a very good example. Again when in doubt, don't use!. You may end up with a stylistic mess...
Layout: Plenty of negative space, strong grid systems.
Photography: Is a highly predominant element in modernist design. Both silhouetted and full sized. Photographs can be black and white, colour or colorised. A special effect often used by modernist graphic designers is the separation of visual material into its colour channels: The master of this effect is Bradbury Thompson and I would advise any budding designer to take a long look at his work - not only for the usage of photography but also the general layout, visual combinations and typography.
Shapes: The typical whimsical retro shapes, such as the kidney shaped elipses may sometimes be too strong for the stark simplicity of modernistic design, can however be used in discretion to great effect. Consult previous link on Modernistic design as to how best to use these elements. Rectangles and trapezoids, in general are a safer bet.
Plugins: The 1950's seem to me an opportune time to go into the usage of Photoshop plugins>>>>

Samples:

Pop Retro
Keywords
Typography: A spoofy, caricaturised version of the above mentioned hard serif fonts that is extremely dynamic and youthful. There are some wonderful contemporary interpretations of these as well. The hard serif fonts are also very much in evidence. Type can be colourful. Again era specialised script and brush script. The cautions above apply to even a larger extent: There are very ugly brush fonts around, be careful! And also be careful of script fonts: These may have Baroque and not 50's retro references.
Layout: A loose layout, with a very loose grid. Type and type blocks as well as columns can be at angles.
Visual material: Plenty of illustration and era specific clipart. Again usage of photography, especially silhouetted photos. Channel separations are also widely used.
Shapes: Go for broke! Use your imagination. This is vector heaven. As long as you stick to basic premises of fun and humour you really cannot go wrong. These shapes will work alone and in combination. Especially look at the work of Miro for inspiration.

Samples

Plugins