photography is many things to many folks. as such, i would never dream to offer advise on 'photography' as a whole. what i can do is share my own, personal lessons as a photojournalist and documentary photographer. i will leave the business end of it out as this doesn't seem the objective here.
as someone who photographs people almost exclusively, the most powerful element has proven to be ACCESS. not lenses. not films. not sensors. not megapixels. access.
learning to develop trust, knowledge and empathy has done more for my photography than anything i have purchased, studied or emulated. making and maintaining relationships, often without a camera in my hand, has become paramount. having the trust and cooperation of the people i photograph makes for great images. allowing them to be an equal partner in the exchange and caring about them has entirely changed my photography. more so than anything i could have purchased.
in my humble opinion, this is the barrier for most photographers in the particular niche i occupy.