My only advise (I have only made a few salt prints), is to expose and develop your negatives for the process you are using. If you need more contrast in your prints, get more contrast in your negatives.
Most processes have ways to adjust the contrast, but often it comes at a cost. For example if one is using Potassium chlorate to boost contrast for platinum/palladium prints, it works fine until you need to boost contrast so high that the amount of Potassium chlorate starts to cause grainy images.
I believe fine-tuning one's negatives for a particular process is the best way to go.