One thing that seems to plague people with Asperger's (according to some reports and my own experiences) is handwriting. Handwriting involves use of coordination and spatial skills that we can have difficulties with. Currently we are working with my son on his issues.
When he writes his name on a piece of paper, he has trouble defining it inside the lines. It comes out large and multiple words wind up overlapping. He finds this frustrating as it's not intentional. It's a natural difficulty with his condition.
The only real cure is practice. Practice at slowing down to apply skills to paper. Occupational therapy can also help and he does work with an OT. He told me this morning that someone in class told him about lines in a way that's helping him. He couldn't explain past that, but we'll take what we can get.
My own handwriting is horrendous. What's funny is that I'm an artist and I like to draw fantasy creatures and super heroes. I can do a fair job if I put enough time into it. So what's the deal with my handwriting? I have to slow down. Even then, my hand has lost some of its steadiness in time. My drawings have suffered as well as my handwriting.
Some good ways to help your child include working with teachers and getting large print practice workbooks for home. Start with a single line and practice keeping it between two other lines. As he gets comfortable with this you can add lines or letters to practice with. Even so, our natural impulsiveness makes us want to go faster than what our hands can do.
Most importantly, it is controllable and correctable with time, patience and practice. That doesn't mean he will develop beautiful handwriting, but it can get better.