* What kind of vehicle is it? (Make, model, year)
* When does the shaking happen? (Idling, accelerating, decelerating, at a specific speed?)
* How long has it been happening?
* Have you noticed any other symptoms? (Strange noises, loss of power, check engine light on, etc.)
Once I have this information, I can give you some possible explanations for the shaking and suggest some things to check.
