Voter turnout is lower in the United States than in most other democracies. A few of the countries that do better than America have compulsory-voting laws, so comparison is difficult. Nevertheless, voter turnout should be higher in a country that prides itself on its democratic traditions.
Voters want to know that their votes count for something. In presidential elections, that is usually not the case. The problem is that the Electoral College awards all its electoral votes to the candidate with a majority. Because of this, voters in strongly red or blue states often feel that voting is a waste of time. For example, California reliably votes Democratic, so Republicans in that state are not motivated to go to the polls. Presidential elections are usually decided by Florida and a handful of other swing states. Eliminating the archaic Electoral College would solve this problem and make presidential elections more democratic.
Another way to enhance voter turnout would be to change the election day. The US holds its national elections on a Tuesday in November in even years. Elections should be held on weekends, or the weekday should be turned into a national holiday.
American elections are usually too long. For instance, presidential elections last for about two years. The public gets tired of elections ads and election coverage on TV, so the length of campaigns probably reduces turnout.
Additionally, higher voter turnout usually benefits Democrats, so Republicans are usually less enthusiastic about steps that could enhance the public's participation in elections.