The best example I found is Moses and the Israelites against the Amelekites, whilst Moses' hands were raised, the Israelites were winning the battle, but when his hands came down, the Israelites started to lose (Ex 17:11).
The Psalmist shows us how to praise the Lord with our arms and hands raised - "Hear my cry for mercy as I lift up my hands to your most holy place" (Ps 28:2), "... in your name I will lift up my hands" (Ps 63:4), "... may the lifting up of my hands be like the evening sacrifice"(Ps 141:2), "... I spread out my hands to you" (Ps 143:6).
As a final example, and our only command, is from the Apostle Paul. "I want man everywhere to lift up holy hands in prayer" (1 Tim 2:8).
Why then should we lift up our arms and hands? We have all seen the war films where someone is captured, up go their arms and hands in surrender, the become prisoners, they surrender to a greater power - so do we!! We surrender to God. This is a sign of our supplication and humility. Paul said he was a prisoner for Christ (guess what? - so are we!!)