I offer an answer in my weekly post for US News & World Report. The key is recognizing that the two major political parties have no intellectual coherence, so centrists can't just be about splitting the difference of every issue.
A compromise between two intellectually incoherent parties is just a mess.
As I note in the post, "Centrists ought to stop defining themselves using a political spectrum that no longer has any meaning. Instead, the political middle ought to start from scratch, building a set of guiding principles that: 1) make sense; 2) appeal to the large and growing segment of Americans who are disaffected with the two-party system; and 3) embody the tools necessary to deal with America's most serious policy challenges."
In that spirit, I've compiled a "centrist pledge." See if you would be willing to take it. Read the full piece here.