There are several tips for making handles that will not crack at the point of joining or fall off after firing.
I use Martha Grover's paper joining slip. These are the directions for making this slip.....
1. Make sure that the mug and the handle are a soft leather hard. The clay should not distort when you are attaching.
2. Score the mug and the handle joint liberally and paint joining slip on each part.
3. Move the clay from about an inch up the handle toward the mug with long, flowing strokes... ( no short choppy strokes)
4. Allow the handle to dry SLOWLY..... I cover and uncover with plastic for two days.
5. Sometimes I trace around each point of attachment with a pencil....the glaze will pool in this area.