Took a stab at the dinosaur archer. First of all, try not to work on a very saturated background - it skews your perception of colours and tires your eyes. Second, zooming out and/or mirroring the piece every so often while working helps you notice mistakes easier (you may know this already, but it can't hurt to mention it).
Many of the colours you're using are very similar - try to use the least amount of colours you can get away with. This improves readability and makes it easier to adjust things later and animate. Don't be afraid of contrast - at the size you're working, subtle changes in colour are more or less invisible. Also, try to vary the hue when shading - in general, shadows are less saturated and tend towards the complementary colour of the light. For example, if the light is yellow, the shadows will have a blue/violet tinge (this depends on the colour model you're using). Additionally, if the light is warm, the shadows will be cool and vice-versa.
Your shapes are very blocky - even a single pixel will make a world of difference in a small image. Try to focus on how a particular pixel affects the shape as a whole, not just the pixels near it. When adding small details, it's better to just hint at them using a pixel or two instead of trying to draw them as they actually look.
Why is the archer sitting so far back? They would fall off the moment the dinosaur started moving! If you did it to keep the bow and the dinosaur's head from overlapping - there's no need to. In a larger image, you'd have to be careful to avoid tangents, but they're not really a problem here.
Regarding animation - if you're interested in learning it, I suggest getting a book called "The Animator's Survival Kit" by Richard Williams and studying it. It's one of the most useful books on the subject I've found and explains it far better than I ever could, especially in a single forum post. Although it deals with traditional drawn animation, the fundamental skills are also applicable to pixel art. Good luck!
