I can't claim to be an expert, but I can tell you how it went in my case. I was self-taught, then took a lesson midway through my second season. Discovered I had developed a HUGE list of bad habits, plus was simply unaware of some techniques. One two-hour lesson (group lesson but I was the only student, so effectively a private) made an incredible difference. I managed to unlearn all my bad habits and am a far better snowboarder for it.