Not sure if it's me, or if their necks are just a bit stretched out farther than canon ponies' are. Also, on your Fluttershy sketch, the curve of her mouth needs to be a bit more.. angled. I'm not sure how to describe it, because I have trouble with such a shape as well. Their ears also look a bit smaller than usual. Legs are a bit thin, also, but these minor differences are what give your drawing style uniqueness, so I wouldn't worry about it.
The only actual suggestion that I'd say is; Go back and thicken the lines a bit more. Not darken. Thicken. Because if you look at the actual ponies' artwork, their outlines are rather thick. I suggest looking at a reference picture for this, though, because sometimes certain areas call for thinner lines (like the ears) than others (say, the mane outline). This may or may not be a good idea, because you've already drawn the ponies, so it's up to you to decide on it. They're still good either way, so good job, by the way. Very good job on Applejack's dress, I must say, as well as good eyes on all of them. I personally have a lot of trouble drawing their eyes, trying to get that perfect round shape. On your Fluttershy sketch, though, the eyes are a bit off, but Fluttershy's eyes are weird, so I don't blame you, honestly. I'd probably do much worse. Keep up the drawings, because you capture the MLP style very nicely.