"To plan something" means to make detailed arragements for something you want to do in the future. "To plan on something/to plan on doing something" means to intend or expect to do something. So in this case you case use the word "intend" instead of "plan". We hadn't planned on going anywhere this evening. = We hadn't intended to go anywhere this evening. In your case you think over every detail/every step how to achieve your goal so we must use the word "plan": How to plan my goal?

how to plan my goal is correct,...... the meaning is your asking for what do you want to plan your goal

How to plan my goal/goals is correct