In order to generate a planetary dynamo we need three things-
1. Conducting liquids 
Edit
These liquids are metallic in nature.
Non metallic substances can be brought to a condition where they would act as metallic substances.
2. Rotation Edit
They cannot stay be fixed with respect to the parent star/planet. They shouldn’t orbit a host planet/star with one side facing the host at all times.
Planets that escape their star's orbit and wonder alone are not taken into consideration because they must rotate with respect to a local gravitational body.
3. Convection Edit
The planet must have enough internal heat and be far enough from its star to be heated at the core and cooled at the surface.
