In my younger years when I was ambitious and trying to please, I would put in about 60 hours a week and get paid for 40. If you do the math ones hourly rate plummets quite rapidly under those conditions.
By simply living long enough to figure it out, I saw that it was actually not getting me anyplace. First rule of thumb...if you don't think you are worth something, no one else will either. It is a big chance and it doesn't always work unless you really are valuable, not just think you are.
As I got more mature (and by that I mean old), I no longer cared if I was valued or not. Hence, I just do 40 hours now unless there is an emergency and I will then give whatever time is necessary, but as a normal weekly thing...about 40. I now make more money then I ever did, feel more job security then I ever did and am a lot less tired.
WARNING: The above statement was not in anyway an endorsement for fluffing off at work, especially if you are just starting out, and I will deny that I ever said anything if something bad happened and swear that someone else wrote this post using my name. Nope, never even saw this thread.