Trigger event if task is aggigned to user

I want to send notifications to Users if they have been assigned any task in the workflow. Suppose I ( ) started a process by filling some information-form and the next task will be assigned to user for reviewing the submitted form. So is there a way to trigger event just after filled the form so that I can notify that he has got a task. ( Yes I can achieve this with script task but I have to put a script task after each form and for every client ).
Please let me know if you have not understood my requirements.

Why not using an execution/task listener into the user task itself?

There, when the task is assigned, you can send the email