While you will need to focus on his particular areas of concern, I would advise you start from the very basics -- the firsts being respect of your space and giving to pressure. However, if his destructive behavior (re barn, fences) has continued after he has been gelded, I'm not sure how you would correct that behavior. Hopefully there is a reason behind it that can be worked through.
I learned through trial and error as well, and it is long and very disheartening when you realize that you messed up something in the training. That requires going backwards several steps to "untrain" your own mistake. Not easy for all involved.
Read, read, ask, listen, watch, learn what to watch for... This means watching other horses and trainers/riders/hands, not just yours. If you can find a trainer to guide you that would be most beneficial.