Need more info.
Have you gone to an optomotrist about it? What did they say? (There are actually several types of night blindness)
The bad news: Not a real lot you can do.
Make sure you are getting enough vitamin A.
Try walking in a safe area (your living room, for example) with the lights off. With just ambient light, you'll start forcing yourself to notice more.
There are some eye-exercise systems out there that may help, but the research is pretty sketchy. Still, file palming and gabor techniques can't hurt, might help.
@daniellep, your query reminded me of some text in an old post by Jack Kruse...
i can no longer find the post on his site, but here is an archived link;
the relevant bit relates to Vitamin D3 and Vitamin A levels
& here is the text (bolded by me);
fake it till you make it