A country in which there is no constitution guaranteeing basic human rights is one example of a country that is not going to have a successful democracy. If there are no constitutional protections, people can easily vote for a dictator, who can then suspend democracy, either suddenly or gradually, by depriving people of their rights, for example, the right to free speech or the right to assembly. Not having such rights completely defeats the idea of a democracy.
A country that does not have a literate citizenry is not likely to thrive as a democracy, either. People cannot make choices if they are lacking in information about their choices. In the United States, we might not have as high a literacy rate as we could or should, but most people can read, and so they have at least the capability of learning more about the candidates. (Television ads are not very informative.)
A country that wants to be a theocratic democracy is going to run into some problems, too, because it is likely to repress the religious freedoms of minorities. This has become of concern since the Arab Spring, as countries are overthrowing dictatorships and trying to instate democratic institutions, since there are efforts to incorporate religious law into the framework. Minority peoples have grave concerns about how they may fare, and many are fleeing.