The golden ratio is 1×1.6, you could make the X 160 tall and 100 wide, but it won't be interesting yet. Exes are symmetrical so you're going to have to warp it to make it dynamic like above. I recommend finding a good x in a font or drawing one, then playing with it to see what's possible. Separate and offset each leg, round corners or no, put it in the rotate tool. Place it over the golden grid and line things up. Look up "X logo" in Google images and get ideas. Play end experiment, make copies and try new effects.