I believe they should be firm if you squeezed a pair of spokes. Go around the entire wheel this way. I'd say if it feels like you might round off the spoke nipple then you should consider another method like loosening the opposite side. I've just mastered the art of straightening my back wheel which seems to get bent often enough. Maybe you need a heavier duty wheel. I know on my dirtbike I can almost never tighten a spoke too much.

Cannondale