There are a number of postures for prayer described in the Bible, but it doesn't make rules for how our body must be to pray. What God looks for is the attitude of our heart. We can try out various postures, and decide which one helps us have the best attitude in our heart.
Some churches mandate that one must kneel to pray in their church, or at home. That might help some to have a more humble attitude, but it creates unnecessary worries for those who are sick or unable to kneel. Again, because in some religions posture for prayer is dictated, we need to review some of the postures for prayer in the Bible and determine what we can learn about them.
We see Abraham's servant bowing down before God in worship when he prayed. (Genesis 24) But then servants generally bowed before their master, and pretty well everyone bowed before a king or higher authority. It was a sign of humility and respect and indicated that you were ready to obey that authority. Bowing before God implies that attitude.
King David and King Solomon both kneeled for at least some of their prayers. When Solomon wanted to dedicate the beautiful temple he had built over many years for God, he knelt before all the people assembled and prayed a very long, wonderful prayer of dedication. (I Kings 8:43 and 2 Chronicles 6:13)
Daniel, that captive in Babylon, who was greatly respected by the pagan kings he served, made it a habit or policy to always kneel three times a day, and that beside a window looking toward Jerusalem far away.
We see that Jesus kneeled to pray in the garden. So did Stephen when he was being stoned, and Peter, Paul, and other apostles and elders did so too throughout the New Testament.
King Solomon stood for parts of his prayer, and in some cultures standing to your feet when important people come into your presence is the expected sign of respect. Even today, this is true in countries where the British have had some influence politically and socially in the past. When Handel's Messiah was presented for the first time, the king of England was present and as soon as he realized this was music to give homage to God, a greater authority than himself, and one he submitted to - he arose and stood. Since then Christians in most parts of the world stand out of respect for God when He is worshipped, especially in anthems of praise like the "Messiah."
Several places in the Old Testament describe some people as looking upward in the direction of Heaven, and as if they are expecting God to hear and answer their prayers. This may describe their heart's attitude more than a physical posture, but sometimes we do see someone standing, and looking upward when they pray.
More often, we read in the Bible of someone falling facedown on the ground for prayer. They were feeling extremely unworthy and in utter subjection to God. This was the case for both prophets and kings when they utterly at the end of themselves. You will see this in Ezekiel 9:8, Numbers 16:22, 45 and in 20:6, Joshua 5:14 and 7:6. I Chronicles 21:16, and 2 Chronicles 20:18. Even Jesus fell facedown on the ground to pray in Matthew 26:39 and in Mark 14:35.
You might want to save this posture for extreme times, not every day use.
Lifting up hands to pray, or to sing worship songs, is fairly popular at this time in North American churches. I haven't noticed it outside of church events. The upraised spread out hands are a symbol of confession, openness and being receptive to God, and beseeching God to hear and answer the praying person.
Moses did this in Exodus 9:29. King Solomon did this while kneeling in his prayer of dedication in I Kings 8:22,54. It is also mentioned in these other passages; I Timothy 2:8, Nehemiah 8:6, Psalm 28:2, Psalm 134:2, Psalm 141:2, and Lamenations 2:19 and 3:41.
Any of these postures for prayer can be meaningful to you. As I've shown there are Scriptural examples for all, but no hard and fast rule made by God as to which one you must use. Feel free to try them out.
You may soon discover a few things. One is that once you form a habit of using a certain posture, the discomfort or any embarrassment about using that posture will disappear, and you can concentrate on your prayer to God, and to listening for His answer. On the other hand, you may discover that while at first it forced you to think in a more humble and respectful way, once you get used to that posture it loses that power over you, and you forget. For that reason I find that a change of posture and places to pray can wake me out of a routine that is becoming a rut.
Allow yourself to experiement with postures for prayer, but don't make any hard and fast rules and, don't impose them on others. If you think you get your best praying done when facedown on the ground, don't make others do it. When they are desperate enough to do serious business with God, they will probably find that posture without being told.
If you have been living a transparent (humble) life in your own prayer times, those who watch you may follow your example. That can be good for a start, but don't put them into bondage to your favourite posture. Remember, God looks on the heart. The right spirit or attitude is what He is looking for in our postures for prayers.