His Serial Number is the best way to start, Rafe pointed you to the best link, after you find his units he served in, then you go to the Unit Associations and such.
In my experiences, I came across lots of material that aided me in my search when my Grandpa Joe passed, a Combat Veteran of the Battle of the Bulge. My other grandpa who is still living, likes to tell me storys of his Army years they mostly involve fun times, He served in 45 and during the occupation of Germany.