The how and why of the phases of the Moon - new, crescent, quarter, full, quarter, 
crescent, and new again - remain some of the most challenging spatial 
relationships that people tend to encounter on a regular basis.  The following 
websites have good explanations and illustrations of the process.

http://aa.usno.navy.mil/AA/faq/docs/moon_phases.html
http://online.bc.cc.ca.us/sea/astronomy/nakedeyeb/nakedeyc.htm
http://www.astro.umd.edu/education/astro/moon/phases.html
http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question3.html
http://www.astro.lsa.umich.edu/Course/Labs/moon_phases/moon_phases.html

A helpful synopsis of these explanations is presented in the table below.


IF THE MOON IS IN THIS PHASE AT THIS TIME, THEN IT IS...

             new       1st qtr    full      last qtr
             ---       -------    ----      --------
AT 6am,      rising    below      setting   transit


AT noon,     transit   rising     below     setting


AT 6pm,      setting   transit    rising    below


AT midnight, below     setting    transit   rising


Remember that, just as Earth has a "sidereal day" that's 23 hours and
56 minutes (different from the "rotational day" that's just about 
24 hours), the Moon has a "sidereal month" that's 27.3 days, different
from the 29.5 days it takes the Moon to go through a full cycle of phases.