Start with naadi-shudhi pranayama for 5-10 minutes and then do surya – bedhi pranayam for rest 5-10 minutes.
In naadi-shuddhi pranayama, follow alternate nostril breathing very calmly and with full awareness. First exhale from left nostril and inhale from left nostril. Then breathe out from right nostril and then inhale from right nostril and then exhale from left nostril. This is one cycle. Repeate this cycle for few minutes and proceed to surya-bedhi pranayama.
In Surya-bedhi pranayama, you need to inhale from right nostril and exhale from left nostril. This is one cycle of surya-bedhi pranayama. Repeate this cycle for your further session of pranayama. However, you need to take precautions if you are severely suffering from high blood pressure; so better to start with few cycles only in the morning and evening.
Though pranayam consists of inhalation, retention and exhalation in certain ratio depending upon the stamina of the person, I have not mentioned the retention nor any ratio as I presume that you are new to yoga discipline. But the above breathings are also quite effective as pranayama done in ratio.