How much experience do I need to prepare for medical school?

It's not the amount of experience that matters, but the quality of the experience. You want to have a variety of experience if possible, including some experience at different types of healthcare facility and both long term and short term experience. However, even if you don't have much experience, it's more about how you reflect on it that matters and what you can learn and take away from it. For example, a long term volunteering placement after school at a care home shows commitment as well as understanding of some difficulties healthcare workers face in that kind of environment. It also shows communication skills and an ability to engage and empathise with people of a different generation that you may not regularly socialise with. This one placement can give you a lot to reflect on so it is important that you use every placement you get to its full potential. Quality is always better than quantity.