In general, half of the head of a beer should remain in the glass one minute after pouring. Some beer styles will have a thicker or darker head than others. Excessive head can be caused by a bacterial infection or over priming. No head is caused by dirty glassware, under priming, not enough dextrose or bacterial infection.
Corrective Action:
Always watch your sanitation procedures throughout the process. Make sure the glass your beer is poured into is clean. For a 5 gallon batch, 3/4 C corn sugar or 1-1/4 C DME is usually plenty for priming the bottles. Try adding some maltodextrin powder, wheat, flaked barley or carapils malt to improve your head retention without affecting the color or flavor.