how do you hit a low shot?

How do you hit a low shot when in trees or high winds. I usually have my ball behind my stand but it's still not low enough. Someone told me to hit the ball slighty above the ball but you risk of topping the golf ball.

Ball in about middle of the stance (for long iron). I like to feel like i am finishing with my hands low, and like i am slapping at the ball. Shorten the swing, and shorten the follow through, keep the hands moving low in the follow through.

Ball back in the stand. keep weight more on the left, hand well in front off the ball.

make a nice relax 3/4 backswing and hit down on the ball. normally your ball would go no further that 6 feet with 7 iron.

lower is less lofted club. a 3 iron would go no more than 2-3 feet up in the air

The "how" seems well covered above.  My addition is to suggest you spend a bit of time on the driving range practicing these shots.  Try it with different clubs.  I've been working on building confidence for both a long and short punch out from under trees.

I, and many others I see on the range, have a tendency to want to practice optimal shots and I have to force myself to practice those "trouble" shots.

Those heights don't sound even a little bit right to me. A three iron that needs to go more than 20 yards will get higher than your waist. Unless you're just punching out to the fairway, but if you want to hit a shot then it'll go higher than that.

In high wind, club up and shorten the backswing. With the ball back in your stance, should get a nice low ballflight without losing much distance (i usually have to play 2 clubs up, i.e. a punch 5i for a distance that is usually a 7i).

In trees, it depends on if you are punching out or just need to get under one tree, and don't have any other trees to worry about.

Here's a shot i learned, Take a hybrid or fairway wood, choke down on the club. Put the ball in the middle of the stance, and then hit a very aggressive chip shot, This will just rocket the ball out about 5-10 feet off the ground. I used this a few times when i need to keep it really low. The hybrid works really well because its meant to get the ball up, but it gets through rough alot better than a iron.

Bump and run motion with a longer backswing and normal width stance. Use for recovery only. High winds you are much better off hitting more club, choking down, and swinging easier. Let the club loft flight it lower. If you try and put an aggressive swing on it into the wind, you are very likely to balloon one short. A high spin tour ball will make this even worse.

Like the others said: play the ball back in the stance a bit, open up the stance and use a lower lofted club.