Each face has its frame
The easiest face is the oval face. These ones match any frame. Just the proportions need to be respected. Round faces match perfectly with rectangular frames. These give a thinner aspect of the face. On the contrary, long faces should avoid angular frames and better try oval or round ones. The same for square-faces(jaws). In this case, it's better to choose round frames in order to soften the angles of the face. Triangular faces should wear semicircle frames.
Shade off defects
Frames may help diminish certain blemishes. Large noses look thinner with a dark, simple and delicate" nose bridge". Pierced glasses (without frame) are equally nice. If you have a big nose, you should choose a low "nose bridge" to appear thinner. On the contrary if you have a snub- nose, you should choose a very high "nose bridge" to give the impression of a longer nose and a delicate frame. Your eyes are too close ? Then choose a see-through "nose bridge" or side-pieces embellishments which give the impression of widening. If on the contrary the eyes are too wide apart, then you should choose pierced glasses or a dark "nose bridge".
Colour your eyes
As for colors, imagine that you are choosing your clothes. Take on account especially the color of your complexion, of your hair and your eyes. If you really can't decide what to choose, just take some basic glasses and allow yourself a bit of eccentricity at low prices.