I use a 1HB myself, and was lucky enough my natural swings carried topspin into it. Marius' links are better though.
Position yourself in a square stance, pull the racket back with your left hand, push outward and meet the ball in front of you and a little away from your body. The contact zone for a 1HB is a little further out than 2HBs. Instead of naturally pulling your racket to the opposite side like with forehands, you should be pushing out and up in the direction of where you want the ball to go.
By pushing outwards your racket naturally (by this I mean you don't have to consciously do anything) moves up sharply at the end, generating a small amount of topspin.
I also found another approach on revolutionarytennis.com. The author is a strong advocate of moving into the ball with plenty of linear momentum (moving forward for pace, less rotation and not side-to-side), and said to:
According to him, do NOT straighten your arm. In the picture here it is always at least slightly bent and the first part of the motion should end up at about where you'll meet contact. However, the racket face should be at an angle like:
\
facing the ball. At this point, the author tells you to twist your wrist right here. Hugely unconventional, and I'm sure most coaches and traditional players will disagree with using the wrist right here. Here's the image on the site:
After twisting your wrist you'll follow through. The wrist will produce at least moderate topspin, and you'll be twisting it right about contact. The ball does not go into the net more than a normal backhand, because the slanted racket at first compensates when the wrist brushes up against the ball.
I dunno, I've tried using the traditional post and the other one I mentioned. They both work fine, I usually use the one on revolutionarytennis.com when I'm catching up to a short ball. It works fine.