None, really. For most users,the default settings works very well. Of course, for a newly instaled OS you need to be aware of security - anti -virus, anti adware and firewalls. For me (using X), I would also consider changing settings at the "Local Security Setings"- time before password expires and have to be reset, time period for being locked out, etc. so that you will not be asked to change your password or locked out of your computer at a most inconvenient time. I would also consider creating at least two user accounts with admin. privileges. Other changes or'tweaks' are mostly subjective preferences.
However, perhaps you would like to share the Links to those technical websites as part of this discussion ?
i looked in many different technical wesite such as cnet and they say the same thing that even though windows xp is the present and leatest operating system in pc world but still there is some changes you have to make when you first buy a windows xp pc.so, what's the headche about windows xp (pro,home edition,media center)