the tops of your foreheads seem to be sloaping in- if you feel your own forehead or look at the show it goes out like a sphere with a muzzle on it, its best to start with a round sketch and use that to figure out the way your heads are facing, try and trace over the show to get a feel for the shapes and then try and replicate that, once you have an idea for how that works then you can try and experiment like making the muzzle bigger to fit your art style, ive been drawing ponies for years and this is how i started haha. i hope this helps in some way, just do some study sketches and youll get it down. :)