Slice each clementine in half cross-wise. Juice the clementines with an electrical, mechanical or hand-held juicer, or simply by squeezing with your hands. If you end up using a juicer, you may still be able to squeeze out a little extra juice by hand. Collect the clementine juice in a pitcher or large measuring cup. Remove any seeds by straining with a fork. Strain the juice through a fine sieve if you do not like pulp. Refrigerate until ready to serve. Before pouring in to glasses, be sure to give the juice a stir, because the pulp likes to settle at the bottom. Serve cold.