If you want to take the time zone into consideration, set the default value to:
For a Date field:
javascript:var gdt = new GlideDate();gdt.addDays(-1);gdt.getDisplayValue();
For a DateTime field:
javascript:var gdt = new GlideDateTime();gdt.addDays(-1);gdt.getDisplayValue();
The "getDisplayValue()" is the trick if you want to use the current user's time zone. Otherwise you will get the date in GMT, which could be an issue.
