Basic things first:-
1) Check that the crank is tight on the bottom bracket axle, so tighten it a bit, if you can.
2) Is the pedal tight in the crank? Tighten it up a bit - (clockwise)
3) If click still there, take the crank off the b/b axle, clean b/b taper and square hole in crank, grease the b/b taper, put crank on again. For the first few rides after, keep checking its tightness and tighten if necessary.
4) If click still there after 3) above, take pedal off (anti-clockwise), re-grease thread.
5) As others have mentioned, check that the excess cable on the front mecc is not flicking against the r/h crank.
6) If you are clipless, give the springs on the pedals some lube and while we're at it, check that your cleats are tight in your shoes.
Let us know how you get on.
Ps. In my experience, the most common cause of a single click per revolution on one side, is a loose pedal in the crank.