Use a separate password for each service. To simplify managing multiple passwords, you can utilize a core password that is then "expanded" with information about the service. Assuming your core password is Mb2.r5oHf-0t, you can create a Google password as follows: Mb2.r5_GOO_oHf-0t.
If you use passwords for multiple services, you should at least create different passwords for private, financial and university services.
If you really want to write passwords down somewhere, do not store them unencrypted on a computer connected to the network or on your smartphone, never write them down in combination with the ID, and encrypt them yourself with a method that you can remember and which only you know.
