Sitting deep in the saddle any advice?

All my riding career I have sat up in my half seat for riding, that's just how my barn teaches people to ride.
This summer I decided to go to a horse camp for two weeks and I when I went to see how it all runs the girls that were riding in the advanced group
(which is the group I will be in )
All their butts were sticking to the saddle!

They looked really good at it too! So (to fit in and for advancing my riding skills) I decided to work on sitting deep in my saddle while at camp.

Any suggestions?
Because right now I look like I have a gummy worm as my spinal cord whenever I try to sit deep :P
(i have one more lesson at my barn prior to going to camp if any of you were going to suggest asking my instructor about it)
And of course, I RIDE ENGLISH :P

Sitting deep is all about relaxing. As soon as you stiffen, your butt will leave that saddle. If you are having trouble in the sitting trot, try to tuck your tail bone under you a little more and use your stomach muscles to absorb the trot. In canter there are 2 ways depending on your horse. Relax your body and "scoop" with your hips. Or do a “hoola hoop” motion with your hips, to me this is the best one as your hip moves with all for hooves in this gait and enables you to sit very still.

I don't ride english, but I agree 110% with above. In fact, I just tried out an english saddle during lessons recently, and I found that relaxing your lower back is the one most useful thing you can do. Im used to a big comfy western saddle, and at first I was smacking the saddle in the canter, but honestly, relax and your butt kinda just melts to the seat.

Exactly like everyone said. You want your belly to absorb the shock at the sitting trot. Great for flattening stomachs by the way! And sway like a hula girl at the canter.

The only problem is when I relax my back I look like I have a gummy worm for a spine o.o'

I think it just takes practice to develop those muscles! The more you do it, the more you will build strength and ability to better support your upper body while moving with your horse!

Sounds stupid but to me, the best thing to do when you are learning to sit deep is to take BIG DEEP BREATHS. It helps you relax, helps the horse relax, and as other posters have suggested, without relaxing, you will bounce. Use your heels as shock absorbers. Flex your heels down and take a deeeeep breath.

For me, it also helps to ride the first few minutes without stirrups. It helps open up your hips and allows your body to sit deeper.

Good luck!