Rule of thumb: make the frame fits the style of the photo and the environment it goes in
1. What colour are you trying to emphasise?
Use the frame to reinforce the highlight colour that captures your attention. For example, even though the topic of the following two photos is the same, the style of the image calls for frames of the different style.
Eye colour, skin tone, clothes are also some common factors to consider.
2. How do you feel when you look at the image?
Black frames offer a nice touch of drama while providing your art with a defined territory and personal space. Conversely, white frames work very well with the colourful image and allow for soft emphasis on the artwork.
3. What's the interior style?
Black and white are classic choices that don't appear everywhere just by chance. This duo is the most situationally-friendly when it comes to framing as they work well with most interiors, artworks, and photographs.
White frames on a white wall are especially alluring, giving the illusion of free-floating artwork without borders that's one with its surroundings.
A few words about small spaces
Smaller wall spaces, like the one between your door and a corner of your room, is the perfect blank canvas for hanging framed art. You can visually expand your space by stacking a series of smaller artwork vertically towards the ceiling, but not to the point where it's tough to hang or can strain your neck. Or create a vertical collage picture frame using your photos, and design it to fit in the space.
(Image credits: all in-situ photos are by the fantastic people at levelframes.com. If you live in New York and San Francisco, you should give their framing service a go. )