The button "Configure fields" on first screen, when creating an issue, is always enable for users. The only possible workaround for this button is to set all fields as required/mandatory fields.
I would like to have an option to enable or disable this button for users so they will be not able to configure fields by their own.
In Addition: The workaround of making the fields required doesn't seem to work for all custom field types. For instance it doesn't work for checkboxes in all JIRA versions I tested, and doesn't work for Select List (Multiple Choices) as well in JIRA 6.1.