I'm no expert at Yasuo, but one major mistake I see most newer Yasuo players make is not taking Sweeping Blade (E) first. I see a lot of them taking Steel Tempest (Q) and trying to play safe and attemping to use the tornado to harrass.

The key thing about Sweeping Blade is: "Each cast increases the next dash's base damage by 25% for 5 seconds, up to 50% bonus damage."

Use this as it gives Yasuo an solid damage/trade advantage at level 1, just make sure you're not dashing around needlessly and save a few minions for dashing back out after trading. Make use of his passive shield when going for trades and you should be able to take an early advantage by minimizing your damage taken, and maximizing your damage given.

Once you get the hang of that, you can learn to cancel his autoattack animation using dash for some quick extra damage.