Since his nerf to his sweeping blade ability, always start q on yasuo. If you're against a melee champion such as fizz or zed, try to use the range of his q to harass your opponent as he comes for cs. If you're against a ranged champion try to farm with your q and auto attacks while avoiding harass.

Here are some stats from my account: http://prntscr.com/4qnr1h
As you can see yasuo is my most played champion and he helped he carry my team from silver V to plat V.

When you've reached the mid game you should have a statik shiv and berserkers greaves and/or a vamp scepter. Once you get your ultimate you should be looking to either roam or attempt to make plays against your opponent. Yasuo hits a large power spike once he completes his statik shiv and another when he completes his infinity edge.

https://www.youtube.com/watch?v=-vdVTAhzq3U
Here's just a video showing some clips from one game using yasuo and another on lee sin. There are some things you can learn from this :D

When you're teamfighting with yasuo try to avoid starting off the fight and getting bursted down. When you're teamfighting try to follow up with your teams engage unless you're able to knock up a priority target. See if you can synergize with your teams knockups, if your team has no knock ups try to kite backward and hit a priority target or a group of enemies with steel tempest (q). Yasuo is really good at chasing enemies and cleaning up fights so try to make sure you don't die early unless you feel you can follow up effectively with your teams engage.