If two or more teams are equal on points on completion of the group matches, the
following criteria are applied, in the order given; to determine the rankings:
a) higher number of points obtained in the matches among the teams in question;
b) superior goal difference in the matches among the teams in question (if more
than two teams finish equal on points);
c) higher number of goals scored in the matches among the teams in question (if
more than two teams finish equal on points);
d) superior goal difference in all the group matches;
e) higher number of goals scored in all the group matches;
f) position in the UEFA national team coefficient ranking system (see Annex I,
paragraph 1.2.2);
g) fair play conduct of the teams (final tournament);
h) drawing of lots.
Source:
http://www.uefa.com/multimediafiles/download/competitions/euro/91/87/57/918757_download.pdf