Sight reading is the act of reading and performing music without seeing it before. Sight reading music is considered to be an important skill among musicians. When singers sight read, it is often called sight singing.
When sight reading, you should look for: repeat signs, first and second endings, a coda, or other instructions. Pay attention to key and time signatures. Look for dynamic markings (forte, piano). Look for accidentals, key changes, and rhythms. Look for similarities in the music. Read ahead and hum when practicing.
For more information on sight reading, visit this site: http://www.vocalist.org.uk/sight_reading.html
This picture was taken by Caitlin.