  The Kepler spacecraft has collected data of high photometric precision and
cadence almost continuously since operations began on 2009 May 2. Primarily
designed to detect planetary transits and asteroseismological signals from
solar-like stars, Kepler has provided high quality data for many areas of
investigation. Unconditioned simple aperture time-series photometry are however
affected by systematic structure. Examples of these systematics are
differential velocity aberration, thermal gradients across the spacecraft, and
pointing variations. While exhibiting some impact on Kepler's primary science,
these systematics can critically handicap potentially ground-breaking
scientific gains in other astrophysical areas, especially over long timescales
greater than 10 days. As the data archive grows to provide light curves for
$10^5$ stars of many years in length, Kepler will only fulfill its broad
potential for stellar astrophysics if these systematics are understood and
mitigated. Post-launch developments in the Kepler archive, data reduction
pipeline and open source data analysis software have occurred to remove or
reduce systematic artifacts. This paper provides a conceptual primer for users
of the Kepler data archive to understand and recognize systematic artifacts
within light curves and some methods for their removal. Specific examples of
artifact mitigation are provided using data available within the archive.
Through the methods defined here, the Kepler community will find a road map to
maximizing the quality and employment of the Kepler legacy archive.
