sailing drills above are a good idea. Also get comfortable with coastal piloting/navigation, chart plotting, laying out a course, fixes, judging speed, adjusting for current, "sailing where the rocks aren't", steering a compass
course, taking bearings off shore objects.
Weather monitoring and forecasting too. Reefing/unreefing. Estimating fuel
and water consumption. Radiotelephone, how to use. Recognizing running lights
of other vessels, dredges, etc.
The list never stops really. But at some point you just go out, and learn the rest from the school of hard knocks. What you do before then determines if the knocks are going to be learning opportunities rather than fright and panic.