Before starting with Mastering ServiceNow Scripting, it is advised that you have a good understanding of the ServiceNow platform. It is advisable to have a system administrator certification or similar knowledge, and to be aware of forms, lists, and tables in ServiceNow. You should also be able to comfortably navigate around a ServiceNow instance.
Some knowledge of JavaScript will be advantageous, but is not compulsory as the examples given will give you script to try and get started with.
It is advised to have a ServiceNow instance that you can use to try out the examples and create some scripts of your own. If you do not have an instance at this point, personal developer instances (PDI's) can be requested from ServiceNow for users who would like to improve their ServiceNow skills.