Here is my five minute drapery tutorial. I am not an expert at this and usually I cheat, so if anyone more experienced contradicts me, listen to them instead
I'm not sure if you constructed your character before you started drawing - he's pretty solid-looking so I guess you did. But the key to drawing clothing is understanding what is underneath that clothing, since cloth reacts to whatever it's draped around.
Basically you need to know what the character looks like nude, then figure out the contact points with the cloth - that is, where the cloth is pulled tight against his body, either by gravity or by some other force. Sometimes this requires some thinking and real-life posing to figure out. In this case he's just standing there so the only force pulling the clothing against his body is gravity. And since it's gravity it will be pulling straight down. But the contact points on the shoulders are also pulling against each other a little bit.
Try marking the contact points and the "flow lines" the first couple times you practice this. Once you get the hang of it you'll be able to do that step in your head without having to draw it.
