NO! I Can't Say It.

The in ability to say no. That is my number one problem in life. I want to help everyone all the time. But what happens is that my projects all suffer. I always put my homework off or laundry or dinner to say SURE when a friend needs help. That is usually fine except when I run out of hours in the day and I have no time left for my stuff! How do you balance helping out with your own needs?