Firstly, think about where you are planning to place your finished work. Certain elements can affect where you place it such as light, humidity, rain or heat. If your piece is going to be placed outside, take into account the environmental issues than can affect it. Mosaics can adhere to many different surfaces. Outdoor pieces can be done on Ceiling board or clay pots. Indoor projects that are done on wood can also be placed in a sheltered place outside where the elements can't affect them too much. Naturally after putting so much work into a project we would like it to last.....
Lighting can affect the look of your work, especially if you have used a lot of mirrors. In the sun, you will get blinded periododically. Color choices become important once you have decided where to place your work.
when selecting your project you will need to decide on that kind of background you will be working on, i.e wood, metal, clay. What glue or resins you will use and which tiles are appropiate for the selected area. Glitter tiles fade when placed outside in the sun.
Having considered all your options, please bear in mind the following:
Using mirrors when the lighting condition is glaring can become a problem (that house number in the morning sun?).
Mirrors can be effective in adding interest to the mosaic in indirect lighting conditions.? With less light, intense colors that have been combined may lose that vibrance and intensity without the necessary light.
Setting a mosaic at an angle can help take advantage of the light available.
Darker locations may require colored grout and intense planning to bring out the best in the final output.