Good morning, ladies! I found some guidelines on a website that I thought might be helpful. Some stuff you may already know, but I'm copying and pasting the entire thing just in case. Hope it helps!
"In order to analyze your chart properly it is best to have the most accurate data recorded. Your basal body temperature will be most reliable if you follow these guidelines as closely as possible.
Take your temperature just as you wake up in the morning, before doing anything else. You can not get up, sit up, walk around, go to the bathroom, eat anything, drink anything, or engage in any kind of activity (even shaking down a mercury thermometer can skew your temperature). Keep your themometer at your beside along with a notepad to record the temperature and the time it was taken. If you use a mercury thermometer, shake it down the night before.
Take your temperature at the same time every day. Yes, even weekends and holidays. Set an alarm - you can always go back to sleep! This is very important as your resting temperature increases by approximately 0.1° every half an hour and so could skew your chart.
Take your temperature after at least three to four consecutive hours of sleep. (To get a more reliable result at least 5 hours is preferable)
Take your temperature using a special BBT thermometer. You can take your temperature orally, vaginally or rectally. Just be consistent throughout the cycle.
You should use the same thermometer throughout the cycle. (If you buy a new one, start using it on cycle day one of the next cycle.) If your themometer breaks and you must use a new one, make sure to add a note of this on your chart.
Don't get upset if you oversleep or forget to write a temperature down (or miss a day all together) In most cases one or two missed temperatures won't make ovulation undetectable. (Especially if you are checking multiple fertility signs like cervical fluid, cervix position or using ovulation predictor kits or a fertility monitor). Just do the best you can.
It is also advisable to mark in the notes section on your chart days when your temperature may be unreliable due to illness or alcohol consumption etc.
Ideally, you should start charting on the first day of your period, and continue to take your basal body temperature every morning throughout your entire cycle. Every day, record your waking temperature, along with the time that you took it."