You know, Yasuo requires a high skill level top play, hence why he is only played in high competitive elos such as Bronze V. In order to maximize your damage output, you need to stay alive and therefore you need 3 revival quints and the 30 points in the defence masteries. As well, your windwall will save your life many times as well as deal a massive AOE stun knockup and pairs nicely with your ult, hence why you need to max your windwall first. Now, when you first enter the game remember to buy the doran ring and 2 pot move in order to maximize your damage on your dash (E), hence why you will be maxing it second.