>> How can I best maintain my XP Professional? <<
No one can assure that if you follow some procedures your windows XP won't be broken. Reviving it it's more difficult than in legacy windows versions.
Anyway, although your 1 line question is so vague, I'd give four lines answer. Run disk cleanup, defrag. Test your PC for viruses and spyware. Have a firewall as a minimum line of hacking defense. Download and install from windows updates the security patches. These are very basic advises.
Trying to unweave, unwind, unravel
And piece together the past and the future,
T. S. Eliot
How can I best maintain my XP Professional?