Ah, yes. Ordinarily I'd be thinking in terms of conservation of momentum, coefficients of elastic restitution, trigonometry and so forth, drawing imaginary lines, consulting my book of log tables and stuff before taking a shot. Get a couple of pints down me and the method changes to "Just twat the fucker as hard as you can, and something's bound to go down a pocket."
Funnily enough, the second method is usually more successful. I guess this is because all the questions in physics exam papers, even the ones about bodies colliding, are carefully contrived and feature assumptions that do not hold in the real world (like cue balls that are a fraction smaller and lighter than object balls, thus subtly altering the angle of transfer of momentum -- it's actually slightly upward, whenever a small ball hits a larger ball -- and the separation velocity; tables that are not perfectly level; or cloth with a nap and therefore whose coefficients of static and dynamic friction are vectors, not scalars; hell, even sane estimates of how much energy actually gets conserved in a collision).