"Where he sets his sight, he puts the bullet." This comes from the great Western gunmen who were excellent shots. I.e., it has its literal meaning, which then extrapolates to "accomplish the objective you set up to accomplish". Somebody wants to buy a car... looks over different models, but he "has put his eye on one specific one"... and finally buys that one... One wants to go out with some specific girl... and ends up marrying her... One wants to get a specific job position, and he does whatever needed to achieve it, and he is successful in doing so. Normally, it has the connotation that it is “fast”, i.e., the intention to get there without delays and getting your objective accomplished “fast like a bullet”, “right on target” “right on the money”.
To "be right on the money" means generally to do something without flaw, absolutely correctly, and without even the slightest error. This idea goes with the precision of being able to place the bullet exactly where you put your "eye" (your sight).
“Keep your eye on the ball” gives me a slightly different idea, more of a connotation of “keep focused”, as an advice, and also being more careful. I would say, “Rafa Nadal es el mejor tenista de la historia en tierra batida: donde pone el ojo, pone la bala... aunque ahora tiene que andarse con cuidado (keep his eye on the ball) en Roland Garros. The expression “donde pone el ojo, pone la bala” gives more this idea of absolute certainty and ability to achieve one’s goals and objectives. (Like Kobe and Pau Gasol... where they put their sight, they put the 
) 