The first and simplest mindset that people latch onto is dead wrong.

"It's going up, I better buy a whole bunch and sell that when it's done going up!" Nope, nope nope. Sell a portion of what you already bought when it was low.

"It's going down, I better sell everything and buy it back when it's done going down!" Nope, nope nope. Keep some cash on the sidelines to buy when it goes down. Not sell.