Prof. Henry Louis Gates Jr. answers this question for a prospective black member. 

Encouragement and specific suggestions for taking on the challenge of researching African-American lineages. Where and how to start?  The basic methodology is the same as for any ethnic group in America.  Working backwards and documenting births, deaths, and bloodline connections as you go. However, researching African-American lineages presents a unique sets of challenges and demands special techniques and resources.  A challenging gap exists, which was fostered by enslavement, deliberate destruction of records during the civil war, and a frequent refusal over 400 years to recognize or document multi-racial offspring.  Approach African-American research with the expectations that records can be found and that the patriot ancestor can be any combination of Native American, African-American, and European descent.

Researching Your African American, Spanish, Native American, or Jewish Patriot

Identifies over 6,600 names of African Americans and American Indians who contributed to American Independence.

Identities and individual stories of men and women of color who fought for American independence as soldiers, seamen, wagoners, skilled craftsmen, servants, laborers, etc.