It's important you back up your answers to interview questions like these with some evidence of how you organize tasks and prioritize throughout the day. Anyone can say they are great at managing multiple projects but, that statement has to be backed up with an example. If you're an experienced candidate, you should be able to think of numerous multi-tasking examples from recent jobs or examples from your current one. If you're straight of school and interviewing for an entry-level position, you might want to draw on examples from any internships you've held, or from the classes/assignments/major projects you juggled all at once during a particular semester.