If 2 or more resolutions are available, use the 2nd in the list. This should (usually) be smaller than the desktop resolution, which should reduce noob fail (not realising part of interface is obscured)

#include <QtGui/QApplication>
#include "mainwindow.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}