** I directly used your drawings for this, hope you don't mind....it was the best way I could say what I needed to **
On the first pic, The fur on the tail should probably face the other direction. You also need to be sure that the paws are atleast somewhat in line with each other. Smaller noses and thinner muzzles would help as well, and make sure you don't make the farther ear look longer than the closer one. If it's draw 3/4 view, don't forget the other eye.
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correction 1.jpg [ 49.33 KiB | Viewed 624 times ]
On the second pic, I could only find a few issues. First off, if he/she is supposed to be growling, open it's whole mouth. If not, then you're OK. Also, the bend on the back legs some a little further down, not right at the top. The front legs get slightly too thin towards the bottom, and again tail fur should face the other way.
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correction 2.jpg [ 14.62 KiB | Viewed 623 times ]
And the third pic. The first face is fine, though I woun't put the line at the end of the mouth, but that's just me. On the second face, try elongating it's head just a little bit, and have it's ears face the same direction. As for the third, try to makes it's ears match up just a little more, and shape it's mouth less like a circle, with that expression the mouth would look more like...a rounded triangle or something. A smaller nose would be nice, and a slightly adjusted eye.
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correction 3.jpg [ 22.96 KiB | Viewed 624 times ]
That's the best I can explain, hope it helps. But if you are unsure about part of it feel free to ask me!