Welcome! I apologize beforehand if you are offended that my thoughts of your images do not match those above. However, posting for C&C is an excellent way to learn and grow quickly for both the submitter and the critiquer. So let's get right to it.
First one it was dreary outside yesterday and my faithful sidekick Miss Gabby and I went for a walk around the property to try to find some colour amongst the decay before winter sets in. I like the photo but feel it would do well with more light.
#1 Bright green moss clumps, amidst mostly colorless rock. Very shallow depth of field. Shot at f/4.5.
I think you chose an interesting subject and I would like to see more of it. However, it's so small in the frame that there is little detail for me to enjoy. A majority of the frame is out of focus so there is little else for me to gather detailed information from. Furthermore, the subject is centered, creating a very static, very "central" image.
Next time, I would recommend getting closer (you may need a semi-macro lens, or extension tubes). Include the main clump along with the two smaller clumps on the right. A set of three similar subjects often works well as it is simple, but still interesting as the eye can easily jump from one to the other. You should still use the same colorless rock background as that gives the eye the impression that it's more saturated than it really is, and it doesn't distract from it.
However, keep an eye on tonal values as well. You'll notice that there are several bright white areas on the rock that are the same size as the green clumps. If used in a background or foreground, these will fight for attention. Try to frame it against a darker or midtone area of the rock. Or try all three for experimentation. Work the scene!
This one I love the bird but don't like the overall composition, I needed to get the entire "feeder" he is sitting on and perhaps taking the shot from a higher angle?
#2 The subject is a bird in a feeder, either landing or about to fly away judging from the motion blur and position of the wings. There is a large dark strip on the left side of the frame and the feeder is sitting on the bottom of the frame. The background is a colorful green, where as there are few colors in the plane of the subject.
Again, you chose an interesting subject... a bird in a feeder. Nothing wrong with that. You even "chose" (I'm giving you the benefit of the doubt and assuming you didn't let the camera choose) a slower shutter duration which makes the moving wings almost angelic. Unfortunately, the birds head is soft. That may be a shutter speed issue or a focus issue, I cannot determine which.
Let's set that aside and look at the composition. Again you chose to place the bird center (left-to-right) in the composition, and quite low. This creates a lot of colorful bright green empty space above the bird which is very distracting. Color against colorless fights for attention as it did successfully in #1. Here it is working against you. So be careful of your background color, and brightness. Of course, you should also be always mindful of background content, but I think the "content" of this background is pleasing. You're also chopping the bottom and side of the feeder only to get the bird in the center. This seems illogical to me.
The large black strip on the left seems to server no purpose. The light is coming from the left so I would expect that side of the image to be open, or perhaps even lighter than the rest. I think you should strongly reconsider why you chose to place that there.
Finally, the subject is very small inside the frame. Maybe 5% of the frame is subject which means I can't get any detail out of it. And in the midst of all these other black shapes and bright green backgrounds... it's like the little wimpy kid getting beat up on the playground when he just wants to avoid being picked last to be on a team. STRENGTHEN your subject! Do this through light, color, composition. Think BEFORE you shoot. Think! Seriously, photography is not natural or second nature. We don't see the world in one aperture through a 2x3 box. So it takes thought to retrain our brains to see like a camera does or like a print on a wall.
One more comment, the light on the bird is quite nice, although perhaps a bit on the blue side.
And finally this is my Miss Gabby, I'm rather pleased with this one but again I think some "light" is missing somehow.
#3 You did better here at filling the frame, I'd argue that you maybe you filled it a bit too much. I'd like to see a little more room for the chin at the bottom and for the top of the head at the top. I think tight works like this for people ok, but I don't like it on dogs.
What is the brightest and most colorful area of this image? The mouth. What is the least attractive area of this image? The mouth. I like to call that dangly thing "roast beef" and it's not attractive (although fun to play with

). So either wait until she closes her mouth, or shoot at a different angle which doesn't place so much emphasis on the open side of the mouth.
The light is quite flat because you used your on-camera flash. If you're going to stick with that, the tones in the image have to be taken at face value. The lighter areas are going to be "stronger" to the eye than the darker areas. So find a way to compose to downplay that. OR, don't use your on-camera flash and use ambient light instead to shift the attention from the lighter mouth area to the darker eyes which is where most of the attention should be. If you can get "catchlights" in the eyes, this helps tremendously.
Lastly, I'd either like to see both eyes, or a full profile. Because a full profile looks much better with creative lighting, and I assume you aren't into off-camera flash (yet), let's see both eyes.
I hope some of this helps. I look foward to seeing your progress.