A military records subscription site is Fold3.com
To find a birth date from a death date, subtract the age in years, months and days from the date of death. This is a very close approximation.
Begin with the latest census available and work backwards. Census records have been taken since 1790. Before 1790 you can use Tax Lists and other local lists that might have been compiled according to the state you are researching in.
There are three types of wills: Attested, Holographic and Nuncupative. The attested will is the most common and is prepared for the testator. A holographic will is written by the testator himself. A nuncupative will is the deathbed wishes of the testator, recorded by a witness present at the bedside. All wills must be witnessed.
Always record females using their maiden names.