I started off plaing full lethal but didn't find much fun in it. Since then I try to get the ghost bonus for never getting spotted.
I use tranquiliser gun and that tazer thingy.
I also keep an upgraded assault rifle in my inventory in case I need it for bosses or stuff like that.
Playing stealthy is so much more rewarding I think.
Quicksave/quickload is my greatest tool for achieving a stealthy run though