PL1 has some good suggestions. To expand I would say that the radius of the curve would influence my suggestion. Probably the easiest thing to do, however, is cut out the curve in scrap wood with your jigsaw. Then sand the curve to whatever final shape you want. A flexible sanding strip is fantastic here by the way. Finally rough cut the curve in the final product with the jigsaw again and attach the template to the final product, double stick tape or screws. Then use a router flush trim bit to make the final product match the template exactly.
Flexible sanding strip video:
These are pretty fantastic for sanding curves.