This thread has a lot of helpful content for guide writers, in general.

I recommend that you first of all read jhoijhoi's making a guide tutorial and add in some coding and images. List alternative summoner spells like Teleport but list the benefits and drawbacks of using that over Ignite in depth, and talk about other items such as Ravenous Hydra or Blade of the Ruined King. At the moment the meta is Cinderhulk and tank champions so Blade of the Ruined King is never a bad choice.

• You should introduce to us what Yasuo is good at, and what his abilities do. You go into what to build for him before even talking about his pro's and con's. This guide is meant to be for players who are looking to learn and improve with Yasuo.
  
• Use this video and talk about how you can use Yasuo's Sweeping Blade through jungle monsters if you want to chase or escape. Recommend that you should try it in a custom game first.
  
• You talk about starting with Sweeping Blade with very few exceptions at level 1. Who are these exceptions?

A lot of the information is there, but you need to add a bit more content and make the guide more visual. It's boring to read a wall of text.

Also, it might be good if you explain your runes/masteries choices and also list alternatives for people who don't want to use that setup but want to have the best possible setup early/mid/late whatever.

There are graphic cafe's all over MobaFire. Request one of them to make you a banner for your guide, and they will be happy to as long as you credit them.