Refer to the literature, for instance: Multiple view geometry in computer vision.

9.6.2 Extraction of cameras from the essential matrix

The essential matrix
may be computed directly from (9.11)
using normalized image coordinates, or
else computed from the fundamental
matrix using (9.12). (Methods of
computing the fundamental matrix are
deferred to chapter 11). Once the
essential matrix is known, the camera
matrices may be retrieved from E as
will be described next. In contrast
with the fundamental matrix case,
where there is a projective ambiguity,
the camera matrices may be retrieved
from the essential matrix up to scale
and a four-fold ambiguity. That is
there are four possible solutions,
except for overall scale, which cannot
be determined.

Also, to estimate correctly the Essential matrix, the points should be in general configuration (planar points are degenerate case, see Two-View Geometry (Course 23, Lecture D), Jana Kosecka).