I can give you some help cause dressage is my favourite :)
Ok one of the most important things in dressage to me is your lines, cause if your lines arnt good the judges will notice and you will get marked down.
In your first picture your pony looks like his pulling through your hands, this is obvious because your elbows don't have enough of a bend through them. His probably doing this because its hard work for him and so his leaning on your hands. The best way to get your horse on the bit is to tuck your inside leg against the girth and then put pressure on your outside reign. This will engage him through the hindquarters, which will strengthen him and also stop the hollowing that "hotreddun" was talking about. This also should help to stop him sticking his head up.
Also in your second picture careful not to drop your inside hand, because when you do this you make your outside reign useless aswell.
Id also maybe drop your stirrups one hole cause your really look like you need a longer line in your leg.
You have a really nice upright seat though and you should be proud.
Dressage is hard work but it can be really fun and rewarding. I think you could do really well you just need to put in a bit of work.
If you want anymore help just ask :)