If you feel that you're inconsistent with Yasuo, pay close attention to your play style. If you either destroy or get destroyed, find a pattern. What is it that destroys you? One of Yasuo's biggest strengths is his ability to deal with a variety of different situations. Learn to adjust and adapt to different matchups.
Look at every game as a chance to improve your skills. Learn your enemy in relation to Yasuo. Know their CC and their mobility. Knowing your enemy as well as knowing your champion can help you more than youd think. If you're having trouble landing your tornados look at the cause. Is the enemy dodging or are you just missing?
A lot of players subconsciously repeat the same patterns in their movement. They'll often dodge in the same direction, or path a certain way. Watch for signs of this, or repeated behavior and try to adapt to it. In a parallel sense, you probably subconsciously do the same, so try to be unpredictable. A lot of lower elo Yasuo players have very typical behavior and it'll be difficult for your enemy to best you if you learn to play unpredictably.
There are dozens and dozens of tips to being a better Yasuo player but your main focus should be winning the laning phase. This is your chance to snowball, or just farm up for late. A good early game can lead to a marginally easier late game. One thing to remember: Kills aren't everything. If you're matched up against someone like Malphite or Garen or Darius or other tanks that aren't so easy to kill, don't strive for kills. Go for kills if they're free, otherwise, just farm. You outscale most champions in the game, so focus on scaling. Try to watch your CS closely and don't let your CS fall off into the late game.
Now as far as builds, PD into mallet into IE isn't a bad start. If thats your core then from there out it should be situational. Maybe build a bork if the enemy has a lot of health stacking, or a bloodthirster if you want more raw damage/lifesteal. If your team has plenty of damage, maybe youll want to build more tank and go into a deadmans and then a GA. The possibilities are pretty endless. In the way of builds, try to find a build that you're comfortable with. Different builds promote different play styles. If you're used to a more bruiser-y build, then jumping into a full damage build may not be the best idea. Find a build that works best with your personal play style. With the PD Mallet rush, you have to keep in mind that you're not going to hit as hard of a power spike as you would if you just rushed PD IE, but if you're looking for a more defensive approach, then by all means go for it.
Theres a lot of talks about what builds are best or what items are good or bad, but you're a low elo Yasuo player with a lot to learn. The best thing you can do is find a build you're comfortable with and grow from there. My suggestions for different items to finish out your build path would be Lord Dominiks (if the enemy team has a lot of pesky tanks) Dead Mans (if you find you're getting shut down quickly by AD damage) Maw of Malmortius (helps against bursty AP damage) Mercurial Scimitar (if your enemy has hard CC that shuts you down) Banshees Veil (good against AP heavy teams) etc. etc. etc.
There are so many options its crazy, but this all goes back to adapting. Learn your enemy, learn your weaknesses, then build around them. Hope this helped, and sorry for the essay. If you have any questions I'd love to answer them.