Keywords: mindset, and improving

A mindset is something your brain settles into, perhaps a thinking habit or a cognitive reflex action. We know how difficult it is to change these: with a habit, get rid of "h" and you still have "a bit"; get rid of "a" and there's still that "bit"; get rid of "b" and you still have "it".
So how do you *improve* your mindset? Others have pointed out "fear" and "greed" as the inescapable 2 sentiments as an investor. There's no way to avoid feeling these, unless you're a sociopath incapable of feeling what everyone normally feels. One way to improve is certainly to change the way we respond to these feelings, and the "how"s are aplenty. But that's just changing your response, hardly changing a mindset.
Changing your mindset involves seeing these in a totally different light, so that they trigger more appropriate/profitable reflex actions. Like Warren Buffett's famous quote "be fearful when others are greedy...", your response should not be following the crowd, but charting your own course. Once you've decided on your own course, then you must prepare for that journey, backing up your plans with appropriate resources (putting your money where your mouth is).