History of Christian Prayer I am interested in learning the history of Christian prayer. There are denominations in which people always stand up, take off their hats if they are men, and become silent, humble and serious as a way of expressing respect to God. 

In other denominations, people do not pay much attention to external features of prayer. They don't stand up or hold hands, and they don't even have to assume a proper pose; rather, they can pray simultaneously (not in turns), they can pray out loud, shout, express their joy, anger, contempt, etc. Usually Westerners do not pay attention to posture in prayer. 

Does anybody know whether there were times when people / ministers deliberately worked out decent ways and postures for praying? Can we say that movements/groups like Catholics, Mennonites, or Anabaptist's created their own ways of prayer that can still be seen in some denominations? 

My question is basically this: Why some Christians stand up and assume certain postures, while others pray however they want? How long has it been so? Is it related to the difference between Eastern and Western mentality? Has humanism affected the christian approach to God in prayer?
Does anybody know whether there were times when people/ ministers
  deliberately worked out decent ways and postures for praying?


These innovations in postures and ways of prayers / prayer services exists as far back as we have sources (This goes for all religions and denominations of Christianity).

The use of folded hands most likely came from the Jewish priesthood (as do many other parts of the Mass - in particular those relating to sacrifice). The Mass is the replacement of the bloody sacrifice of the Jews with the unbloody sacrifice where Jesus is the lamb who is sacrificed in every Mass (literally according to Catholic belief).

You also mention standing prayers. In Judaism a prayer service such as the Amidah (The standing prayer) where people stand goes back before  the Siege of Jerusalem (2000 years ago). Since then prayer services have greatly expanded and with that new ways, postures and also for example clothing(largely medieval innovations). 

Other ways of prayer are most definitely deliberate but if we want to find the actual source it'll probably be lost in time or hard to pinpoint which church began. 


  Can we say that movements/groups like Catholics, Mennonites,
  Anabaptist created their own ways of prayer that can still be seen in
  some denominations?


Many of the prayer rituals originated in Judaism. 
Others rituals were taught directly by Christ to the apostles(It is believed that Jesus taught the apostles the way to say the Mass and the other sacraments whilst they were together.) who, in turn, taught them to the new "apostles" (the bishops they appointed).
Others were assimilated into the Church by missionaries as they traveled.

Aside from a few minor differences, the early Christians practiced much in the same way as modern Christians like folding hands; the sign of the cross, the kiss of peace, etc. were all in the Mass from the start. 


  Why some Christians stand up and assume certain postures, while others
  pray however they want? How long has it been so?


Since Christianity exists, there were always denominations / churches with their own innovations of rituals like prayer.