I am a rookie myself, but I think I have a pretty good idea of how Sheik works and how to play her.
The best advice I can give you is to play alot. And play Sheik alot. And play as many people as possible. The more you play, the more control you get and the more you'll get a grip and understanding of her move set.
When you have control you'll feel more successfull with your choises.
If I were you I'd discard the whole "Play to Win" mindset. Replace it with a more "Play to learn". Well I don't wanna force a mindset on you, but this is how I go about it. When I decided to drop the W goal it took alot of weight off my shoulders and I emediatly started improving much faster. We'll it might just not be the case with you
Like I told you in the other thread it's good to know your bread and butter with any character.
You can divide the stock into roughly three.
1st. Dthrow techchase
2nd. Fair setups
3rd. Edge Guarding.
You can call that your cord progression. In reality the game is a jazz duet. So you might get an early edge guard or a late tech chase scenario. You might not get a tech chase the whole stock. You'll push the opponent off the stage while escaping, so none of the above became relevant. BUT go into the match working around the above skeleton is a good goal.
I hope that made sense
"How can I work on teching better"
I think/hope you are referring to the technique callled "Tech" which refers to ground teching i.e. being knocked out of the air then pressing L/R before hitting ground to make a quick handstand animation springing on to your feet (quick) OR holding to a side before pressing and holding L/R to make a "tech roll", instead of tumbling around landing laying down which you have to get up from (slow).
You have a pretty large window where you can press the shield button. I'd say just keep attempting and you'll improve no matter what. Know that you can only attempt the tech input ONCE. If you use the shield button twice in succession you will force a missed/none tech.
"What moves really win with her?"
I think you mean attacks, not moves. Sheik's tilts are great, but I think you mean straight up killing moves in which case you're looking for mainly higher stun aerials:
Fair.
Bair. Uair. Dsmash.
Occasionally Usmash and Nair.
The real winner of Sheik, though, is her edge guarding game.
If you wanna win beast mode one of the cooler combos is the raw FJ weak Bair Fair.
Inspiration for a lifetime:
http://www.gfycat.com/TightBarrenGnu