My son at 5 did everything nature skate,scooter,draw/write right handed but surfed goofy,not for the life of me could I work out why.One day I mentioned this to a mate and he said watch this,stood behind my son told him he was going to give him a gentle push in the back,if his left leg went out first he is a natural or right goofy.We did this a few times and he was a natural so the test results said.Put the leggie on and after a hour in the water he had changed to natural.Living where there are some many right hand point breaks I think my now 19 year old son is happy about that.
If you want some tips,I'd watch and listen to a good learn to surf school and see if you can pick up anything.Back in my day it was pushing him into broken waves then in time unbroken and then he was going down the line.
Good luck its always fun watching the kids at my local getting up for their first time the smile kind of says it all