I have had an idea for making presidents in Africa work. Imagine if an incoming president signs a performance contract with the people stating in very precise terms the goals he wants to achieve. The goals would be created by the president himself and stated in clear numerical terms (eg I will achieve 6% economic growth rate for the next five years; I will cut infant mortality rate by 30% in the next five years, etc.).
At the end of his term, he is evaluated by Parliament according to his promises and if he gets less than say 70% of his goals, he is barred constitutionally from running for office again. This would make all presidents serious henceforth.