  Aims. We investigate a method to increase the efficiency of a targeted
exoplanet search with the transit technique by preselecting a subset of
candidates from large catalogs of stars. Assuming spin-orbit alignment, this
can be done by considering stars that have higher probability to be oriented
nearly equator-on (inclination close to 90^{\circ}).
  Methods. We use activity-rotation velocity relations for low-mass stars with
a convective envelope to study the dependence of the position in the
activity-vsini diagram on the stellar axis inclination. We compose a catalog of
G-, K-, M-type main sequence simulated stars using isochrones, an isotropic
inclination distribution and empirical relations to obtain their rotation
periods and activity indexes. Then the activity - vsini diagram is filled and
statistics are applied to trace the areas containing the higher ratio of stars
with inclinations above 80^{\circ}. A similar statistics is applied to stars
from real catalogs with log(R'HK) and vsini data to find their probability of
being equator-on.
  Results. We present the method used to generate the simulated star catalog
and the subsequent statistics to find the highly inclined stars from real
catalogs using the activity - vsini diagram. Several catalogs from the
literature are analysed and a subsample of stars with the highest probability
of being equator-on is presented.
  Conclusions. Assuming spin-orbit alignment, the efficiency of an exoplanet
transit search in the resulting subsample of probably highly inclined stars is
estimated to be two to three times higher than with a global search with no
preselection.
