This article is from the FAQ, by with numerous contributions by others.
There is no formal definition of what constitutes "national interest".
However INS decisions have established a list of the following
seven factors that may be deemed to be in the national interest in the USA.
(1) Improving the U.S. economy.
(2) Improving the wages and working conditions of U.S. workers.
(3) Improving the education and training programs for U.S. children and
(4) Improving health care.
(5) Providing more affordable housing for young and/or older, poorer U.S.
(6) Improving the environment.
(7) Obtaining a request from an interested U.S. Government agency.