The biggest mistake that I made was doing things that were popular, rather then what was best for my horse. I hung around with a lot of show people and there was certain tack that was "in" or supplements that everyone was using. I followed the trend and bought bits and supplements my horse did not need and saddles that may not have been the best fit. This was before the internet and being able to do research and have access to every tack store on the planet, was not an option.
My advice to you. Keep an open mind, listen to advice, but only follow what you have done your homework on and know is the best decision for you and your horse.