At last - an article on 'How to frame and hang pictures', the definitive article, from Keith Andrews, Art framer

Take cue from your picture: frequently framers will identify a dominant colour within the artwork, print or photograph and replicate it in the frame.  For example, to intensify a sombre-coloured painting I would choose a dark colour. 
Also, the subject can be used as inspiration for the frame.  A typical approach to framing a seascape or beach scene would be to use rough-looking wood with jointed corners and a speckled or whitewash finish

Think inside the box: because a coloured frame has a great presence and is dominant over the painting, it is easy to get it wrong.  But a neutral frame rarely fails.  A white Perspex box frame is very simple and there is an honesty to it because it shows the whole work and all of the paper or canvas.  The artwork has to be interesting, though.  
Conversely, you can use one to elevate something ordinary into a celebrated found object, as you see in museums.  For example, a friend of mine saved all of her children's first shoes and hung them in box frames in her home.

Framing photographs: modern photographs or posters can be dry-mounted (adhered to a backing using heat ) on to a range of surfaces, such as kappa board or aluminium, in ways that complement or match the artwork.  I would choose a walnut wood frame for photographs.  Walnut is a quality hardwood that you can present in its natural form, looks beautiful and works well in most situations.  
Using a tray frame - a shallow box-like frame that often comes unglazed - is the contemporary way to frame a canvas piece, which reveals the edges of the artwork.


Find the best spot: when hanging pictures at home, think about how artificial light and sunlight will reflect off the glazing and affect the artwork inside. Glass with anti-reflective properties can help.
Be careful when hanging in bathrooms or kitchens because of the ambient moisture, and remember that heat from radiators can harm the artwork.
Consider the frame's position in relation to the viewer - are they sitting or standing? Flat pieces are great for corridors, while textural, 3D pieces should be positioned in an alcove, where they are less vulnerable to damage.


Over-hang in small rooms: where space is tight adopt a 'salon hang', where many eclectic works are grouped in a concentrated area.  
In my own house I have a salon-style wall with works based on the theme of love.  The frames are a mixture of modern ones that I have made and characterful second-hand frames that I have bought from charity shops.  
Try painting or distressing a second-hand frame for more character, or take it to a framer who can give the picture a slick finish inside, juxtaposing it with the scruffy frame.