It's hard to know where to start as you don't say what kind of bass tone you like. What players do you like? What kind of music do you listen to?
As discreet said, trial and error. I would start by boosting the mids a bit then sweep the freq control around until you get a tone you like. Then cut the mids a bit and play around with the freq. But then when you get to playing in a band context what you like will change.
Experiment, experiment, experiment.