Use a validated BP device that measures BP from your upper arm, and ensure that the cuff size is appropriate for your arm. See here for a list of validated devices and the correct cuff size for you
When recording your blood pressure
Follow the instructions carefully that come with your monitor. Ensure you are relaxed and wear loose fitting clothes so that you can easily roll up your sleeve.
Avoid smoking, caffeine or exercise within 30 minutes of BP measurements and ensure at least 5 minutes of quiet rest before readings. Sit with back straight and supported, with feet flat on the floor and legs uncrossed. Keep arm supported on a flat surface with the upper arm at heart level. Keep still and do not talk whilst recording.
Take two BP readings at least 1 minute apart and ideally 5 minutes apart twice daily, in the morning and evening for 7 days. If there is a big difference between the first and second readings, then take further readings until they level out.
Initially take your BP in both arms. If there is a big difference between the two let your doctor or nurse know, and use the arm with the higher reading.
Ignore the first day of readings. Record all subsequent readings in a BP diary and calculate the average. Do not round readings up or down and make sure you record both the upper (systolic) and lower (diastolic) readings.
Your doctor or nurse will advise on how frequently to check your BP and how to communicate the results to them. A series of morning and evening readings over 4 to 7 days every 3 to 6 months is typical, more often if medication is being changed.
Your doctor or nurse will advise when and how often you will need to meet up. When you do bring your machine with you so that they can check your technique and the accuracy of your machine.
When should I worry?
If taking your own blood pressure makes you feel anxious or stressed it may not be appropriate for you. Discuss with your doctor or nurse.
Do not worry if you get a one off high reading, but repeat it later. If the upper reading (systolic) is > 180 or < 100, or the lower reading (diastolic) > 100 then contact your doctor or nurse.
Your doctor or nurse will advise on your ideal BP target level, but an average BP of <140/90 (or <130/80 for patients with other conditions such as cardiovascular or kidney disease) is ideal. Let your doctor or nurse know if your average readings are higher than this.
Calibration (machine accuracy testing and adjustment)
To ensure that it remains accurate your device will need to be re-calibrated (tested and adjusted for accuracy) every year or so. Your device will come with instructions as to how this should be done.