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.
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.