The quality also depends on the input file, which means if the file you add has a low quality, and you want to convert it to DVD, then you shouldn't expect a quality increase after a conversion. For DVDs, it's best to add the original file and choose the DVD profile presets. Those presets are standard to DVDs and can be used without messing with settings.
Try using the user guide for the application to learn how to tweak settings: http://www.shedworx.com/midvd-pro-user-guide
