Whenever you discover a new record, if you write the citation right then you will have it.

It is important to always have a citation for a record.  If you do not create the citation at the time that the record is discovered, you may not have all of the information that you will need.

Information that is needed for a citation:  what is the collection (which book, census, historical record, deed record, etc.), where is the record found (if online, the URL should be included), the date the record was accessed, etc.  If the record is from the census, be sure to include the page numbers of the census, as well as the microfilm number and roll number.

An excellent resource for how to write citation is Evidence Explained, by Elizabeth Shown Mills.