How much psi should be in the front shocks on my mountain bike?

I have an older Jamis Dakota mountain bike. It's a hardtail with front shocks. Not sure if the shocks are original (bought it from someone). Is there a general guideline regarding how much pressure should be in those shocks? They seem like they should be a little harder (i.e. they're too squishy), but I don't want to over inflate.