I guess since I'm retiring I can be a little more candid. As far as schooling, specialized in lighting but took set and costume design courses. I did take Izenour's classes but those were far from how to be a consultant. So, forget the schooling.
Like so many things, it's a lot client management. Like promising to make a deadline, knowing you won't, and making the client feel good and happy when you do deliver the drawings well past the deadline. It's a learned essential skill.
A lot is learning how the construction process works - the delivery of the building and the chain of command and floow of paper (or e-docs today) Just the whole process took me 5 years or so to figure out, and I'm still struggling with the electronic methods.
Figuring out what the users want and need and reconciling with budget is probably the biggest design challenge. After that, if you can draft, copy what others have done at first. And stay focused on the end product.
Most of all, I early on adopted the "owners best interest" as the guiding principle. When I get stuck, that is what I ask myself.
And just look and listen and watch.
Probably a few other lessons to learn but honestly, you could be surprised.
As often as I have thought about doing something else, like selling
theatre stuff, I've never gotten too serious about changing. (If I could have changed to being a forest ranger, I might have done that.).