Go to Settings > My Updates and Reminders tab. You have 'Tasks' section where you can choose when will you be updated and how regarding your tasks.
You can be notified for when:
New task assigned to you
Task assigned to you is completed
Task assigned to you is due tomorrow
Task assigned to you due date reached
Task assigned to you is overdue
To receive notification on each event means that whatever happens to your task you will be notified immediately and choosing daily summary means that you will receive one email per day that will contain all changes that have happened since yesterday regarding tasks.
SMS reminder option requires organization SMS credits. More on how to purchase SMS credits in this article.