Whether it is for you or for someone you read for, keeping your readings together will help you in the long run so you can go back and look at any mistakes you made. If your readee (haha) comes back to give you updates, it will be easier to go back to that date for reference. You can keep track of several ways.
One of the ways I keep a track of a read for personal use is in this form.
Date, Day, Time, Weather, Emotions, Health, and the Spread you use. If you are doing a spread for a month, write it for Week 1, Week 2, etc. The same goes for several months but instead of "weeks", you would substitute that for "month". Beside the week/month/year/day, write the name of the card that was received. Then write the card's meaning below that and the result of what happened during that time.
When writing for a week spread, it is better to write the dates of that week. What I mean is if you are doing a read on October 14th (from one of my own records), next to "Week 1", write October 14-21. That way you know EXACTLY how long it will last for that week so you don't get confused.
For the "result" or what happened during those times, it is better to give details of it all. Even if you dropped a pot of boiling water. You may not notice it now, but it will eventually make sense. The card might not say "Bad day coming", but it is possible.
Another way to keep a tarot journal is to do the same outline above but with a section for notes at the bottom. If cards are repeating themselves in certain reads, you need to go back and think about what it means. Write it at the bottom of each read they occur.
If you are reading for someone, make sure to write any contact information at the top of the sheet in case you need to contact them. Write their emotions as well as yours because they both coincide with how things may come about. If you are feeling negative and so is the person, the meanings of the cards and their result may turn negative. So if something goes wrong, you can go back and see.
As far as health, it is inappropriate to strangers "What is your health like these days?" because it is personal business. Instead, ask how their wellbeing is. Are they usually sick, well, or in-between. Usually one can tell if someone isn't well, so if you are unsure they are telling the truth, write that down. They may not be sure themselves.
If you don't want to write during the read, feel free to have someone write it for you or video tape the reading so you can translate it to paper (or in some cases, hard drives) for your record. Ensure the person that only you will video the video.
If you aren't up for writing a journal, take a video of all readers (personal or otherwise) and just write small notes (like the outlines) and file them on disks.
Either way you journal is up to you. Make sure you are comfortable doing it and enjoy your new experience with tarot cards!