maybe people pray out loud just for the reason of actually talking out loud to god- like a normal person would talk to someone, people like to do that with god because it just comes natural.

I don't think their's a right way to pray- I do think they shouldn't be too long though

I used to know someone who ran a christian ministry, and as part of what he did, he invited people to leave prayer requests on his site. he said it himself- he'd not accept prayers that are too long