Supervision really is the key.  The more accidents in the house, the harder it will be to break the habit.  Plus, you'll start to learn the signs he gives you when he needs to relieve himself.  Eventually, he will start to learn how to get your attention when it's time to go.  If you're unable to supervise, for instance if you are in the shower, puppy should be in his crate.  Crate size should be just big enough for him to stand up, turn around, and lay down comfortably.
 
Walk Frequently - immediately after naps, play time, 10-20 minutes after eating and before bed.  Stay with him on his lead.  Don't tie him up or leave him unattended.  I also like the "Hurry Up" command.  He'll begin to associate "Hurry Up" with the act.  This is helpful later in life, especially if it's cold, raining, or you're in a bit of a rush.  All you have to do is voice a little "Hurry up!" when you are outside and you see him begin to circle and get ready to go.  Remember, young puppies cannot physically "hold it" for very long, so expect to go outside every couple of hours, even during the night for the first few weeks.

Praise...lots of praise when he's successful outside - very important!  This is another good reason why you need to stay with him during his potty breaks outside.  Lots of praise will also encourage him to want to get your attention when it's time to go.

Keep a schedule.  Feeding and walking on a consistent basis at the same times throughout the day makes knowing when he needs to relieve himself more predictable.  Also, what goes in on a consistent basis usually comes out on a consistent basis.
 
Punishment - forget it unless you catch him in the act.  If you do, a firm "No!" and an "Outside!" will do.  Then take puppy immediately outside.  Then give lots of praise when he finishes outdoors.
 
Working.  If you find that work makes it physically impossible to walk puppy on regular basis that frequently,  you will need enlist the help of a neighbor or a friend.  Definitely do not leave him alone all day in a crate.  If neighbors or friends are not available, paper training is really the only option.  This involves leaving his crate door open and giving him a confined sanitary area to go and relieve himself.  House training goes quite a bit slower this way and he'll need more socialization after being left alone for extended periods.  This isn't the ideal situation, but it can work.
  
Tips.  Don't use his crate as a punishment and introduce him to it gradually.  You may want to remove the water bowl a little bit before bed time.  Don't use cleansers with ammonia to clean up accidents.