How does one begin to pray?
St. Paul says that "whoever would draw near to God must believe that he exists and that he rewards those who seek him" (Hebrews 11:6). Do I believe that God exists? Really? Do I believe that he is interested in me? That he wants to speak with me? That he wants to grant me good things? The questions are worth asking. So many of us have grown up with the assumption that God "is out there somewhere," but it does not mean much. And we always sort of have a feeling in the back of our minds that he doesn't really listen.
But that is the reality we are dealing with. The One who made everything - and holds it all in being at every moment is interested in me. He wants to give me good things. He wants to speak with me - spend time with me.
So that is primary. We have to believe that he exists and give good things to those who seek him.
Second is a place of prayer.
It is necessary to withdraw from the noise and the bustle and the busy in order to really pray well. That is external - you will want to find a place that is externally quiet - but it is also internal. Don't try to pray in a place when you work or do projects. If there are reminders of "stuff to do" around you, you are going to have a terrible time focusing on prayer.
Third, set a time that is good for you. The end of the day, except for night prayers, is awful. The best time for most people is in the morning after they are clean, dressed and ready for the day. People who are not "morning people" have a bit harder time because by the afternoon, most of us are totally wrapped up in business. Tearing yourself away from work or recreation or family or friends is really hard. And even if we manage to be alone at that time, it's even harder to settle your mind. First thing in the morning is usually the best.
It may require an earlier time of rising. Which, in turn, requires a stable bedtime the night before. (see what I mean about discipline?)
How long should you pray? Every spiritual master I have run across agrees that anyone serious about a life of prayer should pray at least 30 minutes. Half an hour. And, I'll be honest, this is just a beginning. If you want to consecrate your life to God, you will probably want to expand that. But, for started, set yourself a thirty-minute time slot.
Sure, you can pray in any posture in which you find yourself. That is a given, so let's just get it out there. You are, however, composed of body and spirit - and they influence one another. We've all heard of body language and how important it is in communication. Here, you are communicating with the God of earth and heaven, the Creator of all, Savior of mankind, and your personal Sanctifier. How would you sit, stand or kneel in talking to such a one? Kneeling or sitting is usually the best, but even when you get into those positions, how do you sit? How do you kneel? It is best to be reverently comfortable. If you are not used to kneeling for long periods, don't try it at once - maybe start out that way and then sit down. With practice, your praying knees become quite stable and kneeling is not uncomfortable.
So find a respectful position, in a place, and at a time conducive to prayer.