1. Try and keep your upper body quiet. It should still be fluid and roll with the terrain, but most of your movement should be in your legs. Try and keep your shoulders square.
2. HANDS FORWARD! Super key. Practice making a pole plant before each turn way ahead of your body. It'll feel weird but it will teach you to keep your hands up and ahead of you.
3. Feet should be about shoulder width apart, maybe a bit wider depending on your style.
4. Use your edges! Biggest advantage skiers have is that we have four of them. Always have an edge, it's the source of all your control.
5. Keep your weight centered... for the most part. This varies depending on how much snow you're in, how steep the pitch is, how good of an edge you can get (for example if it's icy and you're on your bombed out rail skis), etc. Generally the steeper it is the farther forward you want to be, the more powder the farther back you want to be, and personally if I can't get an edge I like to lean back, but I've skied for a long long time. I think a lot of people would say this is a bad idea, it just so happens to work for me. Most of the time though, your weight should be centered over your feet and your shins should be keeping light pressure on the tongue of your boot.
6. Turning is hard to explain. Chances are you're probably doing it right and this will only confuse you, but turning correctly is so important I'll try and explain... the key comes from always having an edge. You don't want to have to move your legs any more than you have to. You just want to roll on to one set of edges over to the other. Practice ripping in to turns down a steep groomer. Make short turns, not the big long craves you'd use for park. Try to get a rhythm down. If you do it right you should almost be able to feel energy building up in your skis with each turn because there's so much side-to-side and forward momentum simultaneously. It's a really cool feeling. Once you have it you should be able to bounce from edge to edge so that you can turn literally anywhere at any time. As much as I hated racing it helped me a ton here... no matter how shitty and icy it is, or how bumpy it is, or how many trees there are, I can put my skis where I need them to go 99.9% of the time. It sounds stupid but you really should practice this if you can't do that.
That's all I got, good luck and have fun man.