It is good and proper to write out reminders for all matters, both mundane and mitzvah-related, for forgetfulness and death are common. So, it is good for a person to note in writing everything that he does and accomplishes, every transaction that he does, everything that people owe him and everything that he owes others. One should not put off writing reminders not even from one day to the next. Similarly, one should write a reminder for himself of any task that he has to do or say.

I made it my custom that when I drink water before coffee—which is a situation that people commonly forget to recite the Borei Nefashos after-blessing—as soon as I finish drinking the water, I turn the signet of my ring to the other side of my finger or I put the ring on another finger. This helps me remember to recite the blessing. Every person should make similar signs to remind himself and not forget to carry out whatever is upon him to do. 

It is likewise proper to write summaries of halachos that one does not know thoroughly but does need to know. How embarrassing it is for those people who year after year cannot remember clearly whether they are supposed to recite the she’hecheaynu blessing on the second night of Yom Tov in the Diaspora. Or they do not remember the pertinent laws of Shemoneh Esrei, such as when they erred in what they recited. There are many such doubts that come up from time to time, and so, it is a good idea that when a person asks a question and is told a law, he should write the answer down and then he will know what to do and he will never have to be ashamed about that again.