Keep in mind that pixel art is simply a medium. Though it does have its own specific techniques and considerations (pixel clusters, banding, limitted palettes, hardware restrictions, display media, etc), the vast majority of knowledge required to execute a piece of pixel art rests firmly in art theory.
In short, if you want to improve your pixel art, you have to learn art theory.
There's a tonne of things to know in art theory, so a good learning strategy is to reduce the complexity into manageable pieces. Start with the most basic knowledge upon which other topics depend on and slowly build up to the most complex theories.
Following that reasoning, I suggest the following topics, starting at the top of the list and studying them in order:
Line - You will learn about gesture and implying form as well as (most important of all) practise fast, smooth, accurate drawing of line!
Tone/Value - You will learn about contrast and form
Composition - How to arrange line and value in a piece to create focal points and lead the eye
Perspective - Placing subjects within a 3-dimensional space accurately
Anatomy - How to draw people (and with imagination, convincing fictional creatures)
Colour - How to make palettes that harmonise, atmosphere/mood, realistic rendering, using colour within the composition, effect of colour on tone
The ordering after the first two isn't 100% vital. You'll likely reiterate over these topics numerous times.
The best immediate source for learning is books. There's many many many out there, just make sure it's something serious and not a 30-page "How to Draw Manga" style affair. I don't have an extensive knowledge of books, but I can make a recommendation that is "in the ball park":
Robert Beverly Hale - Drawing Lessons from the Great MastersOutside of books (which you really should get), you can scour the web for tutorials, but it's likely to give you eclectic information. The advantage is (if you are impatient, which is something you should work to grow out of if you have any interest in art
) that the length of tutorials are much shorter than the length of books, so you can pick up a few pieces of information, draw for a bit, then find another tutorial.
But let me stress: that is the HARD WAY to learn this stuff.
As for animation, that has it's own body of theory and it's best to grab a book on that, too. It's pretty much impossible to animate convincingly without an understanding of form/volume and gesture, so you're best off coming to animation after you have some experience with those concepts.
That's the basic rundown
EDIT: Oh, and welcome!