The agenda game is one that Smith sees as particularly important. He argues that the success of any presidency depends on the ability of the president to control the agenda and to keep the country focused on a limited number of the most important problems.
As an example of this, many people would argue that President Obama did a bad job of this. They would say that Obama's focus should have been solely on the economy. Instead, however, Obama chose to spend his "political capital" on health care reform. By mismanaging the agenda, Obama made himself unpopular and has lost a great deal of power.
The coalition game is what Smith calls (in the subtitle of the chapter on it) "the heart of governing. What he is saying is that political leaders have to be able to put together coalitions that will get specific bills passed in Congress. Smith argues that building coalitions takes vision and flexibility and the ability to bargain. This is one place where I would argue that his book shows its age. Coalition building was much more possible back in the Reagan era that Smith focuses on. Today's politics is so much more fragmented and polarized that building coalitions is exceedingly difficult.