what ID & PW? if you mean in general, it's unwise to write down any sort of password since anyone could find it.
one way is that you could use some type of pattern in your passwords, just an example that isn't great would be using a password like:
bitcointalk_blabla_123
of course you need to add another element to it, otherwise if someone found out your pasword they'd be able to log in to all your accounts.
there's also password manager software you can use.
thank you so much for your reply.
yes i'm talking about the mean in general, and your suggestion is kinda helpful for me, but there's still a thing that by time goes, i might forget what website address i should login the check or update myself, but i will combine the suggestion by others too. very appreciate your comment, thank you.