What is the the best way to get good World of Warcraft gear?

I am looking to improve my gear on World of Warcraft (level 73 human warlock) and I don’t know what the best method for getting good gear is. Some have said that PvP is the best way, others say instances and raids. I am always checking the AH for good buys but usually never find anything worth spending gold on. Please help, all answers greatly appreciated.