Equilibrium Position
Not knowing what the chemicals in your equation are or what kind of properties they have, I can't tell you how you would measure their concentrations.  

Nonetheless, given:  

$$\ce{A + B &lt;--&gt; C}$$  

If you add an additional, preferably known, quantity of A, then the concentration of B should decrease and the concentration of C should increase.  

This is actually just the real meaning behind your statement that "the equilibrium will shift to the right".  In this case, with two reactants, obviously more of the second one (B) must be consumed by the addition of more A in order to produce more C (shift to the right).  

Again, how you would measure the concentrations of B and C depends on which compounds B and C actually represent.