The best way I've found is to breathe on the neg and let it dry to remove some static. Then just hold the neg by the edges and knock the edge next to the frame you want to print from hard against the baseboard. Give it a good, sharp rap. Turn it over and do the same on the opposing edge. You won't damage it but it's enough to dislodge any dust particles sticking to it. Of course, you'll still get the odd wee bugger that just refuses to move whatever you do.