As someone else has said you need to come in a steep angle, if you try sweeping into the sand you will hit sand long before you want(fat). Cocking your wists as soon as you start your backswing will help in setting you up for a steep decent into the sand.
As I saw on one of the mini lessons on TV(I had never thought of it this way), the angle the club enters the sand is the angle the ball comes out(if you are hitting about an inch behind the ball).
I've been having problems getting the ball out of a greenside bunker with packed sand. The club tends to bounce and I will skull it over the green.
Try to think of hard-packed sand as a thin lie, if you have a 60º low bounce wedge it works well to "pick" it clean and not dig into the sand. If you do not have a 60º then simply use your wedge with the lowest bounce other than a sand wedge and only swing hard enough to send it the distance you require . . . takes a little practice, but relatively easy once you get the hang of it. Good luck!
Lots of good tips here. Also, here's something that helps me: I imagine that the ball is sitting on the middle of a dollar bill. I don't try to hit the ball; I try to throw the dollar bill onto the green.
Great tip JS, I tried this the other day and it ******* worked, JC would be proud of you, if he wasn't too busy fighting the trolls.
Something else to consider is ball position. You need to find how far forward or how far back in your stance to play the ball for your best results. If the ball isn't positioned properly in your stance, you're not going to have much success, regardless of the technique you use.
Also, keep the lower body quiet. Bowing out the legs a bit can help you keep the legs and hips out of the swing.
test the sand with your feet first
hard "packed" or wet sand means an open face and play a cut shot almost ...going into the sand maybe 3/4 of an inch behind the ball
loose sand "fluffy" more square face ..steep straight shot more lined up off the toe going in 2 inches behind the ball
a plugged ball ...close the clubface ....an inch behind and blast it out
all depends on the bounce of your SW too i guess
but these tecniques work for me....to the point of seriously thinking of putting it in the hole let alone getting up and down