How do I use equations of motion ('suvat') to find a missing quantity?

First, be familiar with the equations of motion:s = displacementu = initial velocityv = final velocitya = acceleration (constant)t = time
v = u + ats = ((u+v)t)/2s = ut + (at^2)/2v^2 = u^2 + 2as
Second, identify which 3 values are given in the question (remember that if it's motion under gravity then a=9.8 ms^-2).
Finally, identify which equation to use and plug in the values. Pick the equation that has the 3 known values and the unknown value. Then solve the equation to find the unknown quantity.
e.g. Q) A ball is fired out of a pinball machine at 4ms^-1. After travelling 1.5m with a deceleration of 0.5ms^-2, what is it's final velocity?
A) u=4, s=1.5, a=-0.5, v=?v^2 = u^2+2asv^2 = 4^2 + 2(-0.5)(1.5)v^2 = 16 - 1.5v^2 = 14.5v = 3.81 ms^-1