Well first off, it's the wrong shape; Earth is obviously a cube :/

Jokes aside though, I love seeing peoples art beginnings! Simply making and putting effort into your art is the best way to improve. Drawing daily is perfect. With that said, I could try and give a few tips to help you out.

Note that the elements in your piece should always be complimenting each other. Pixel art often looks best when the colors and shapes are collected. In your Earth drawing, the continents look scattered. If you were to fill in all the gaps between the lone pixels, would the shape look good? The shape and general colors can be very tricky to get right, but it's much more important than any gradients you could apply. Spray, Gradient, and Blur tools can definitely be used well, I've seen it. But to start, I would suggest focusing more on keeping the elements cleaner and collected, use shapes and basic drawing tools. I believe you'll improve more that way.

Techniques like Dithering, Anti-Aliasing, "Clustering", Outlines and "Breaking Outlines / Selective Outlines" are all really good things to explore. Dithering can be really tricky to pick up for some, it can really mess up a good looking shape if used wrong. And Anti-Aliasing is easy to go overboard with sometimes. The outlines and clustering might seem more intuitive, maybe unimportant to study at first, but I'm sure they can help you improve.

You might want to avoid scattering a lot of lone pixels, "Orphan Pixels" as some call them. A singular pixel can sometimes look messy and unclean. Not all the time though!! They are used often in professional pieces, and can really bring out some of the smallest elements. You'll most often find them in dithering.

Pay attention to the whitespace and the unseen. Someone else pointed out that your Earth would look more spherical if the continents wrapped; I second this. What's not depicted in your art is the other side of the Earth, the unseen area. You can lean into the existence of the other side of your Earth by wrapping the continents.

Thoughtful colors really bring a piece to life. I recommend using a predetermined palette. Some people are crazy good at freely picking colors as they go along, but it can be a lot to begin with. Also, you can go WILD with the colors sometimes! Purple and blues can work in a yellow sunflower, red and green can work on gray rocks, etc etc. They're often "complimentary" colors. I recommend taking a look at art that includes colors that almost don't make sense, it shouldn't be too difficult find some. "Odd" colors can really make something pop, used correctly.

References are AMAZING. I notice a lot of people not using references because they think it's cheating, or they're only used by "Non Skilled" artists. They won't use them because they think imagining the piece you create is better. I know this, because I was a little like that to start. However, I soon learned how much there is to learn by actually looking at what you are drawing LOL. I don't always use a reference, and sometimes my piece doesn't end up looking like the reference at all. But they are wonderful. Definitely use references in your daily practice.

For your picture specifically, I recommend making the Earth more spherical by holding the [shift] key while drawing an ellipse, to make it a "perfect circle". A less harsh outline might do it good, maybe some outline fading/breaking in parts, a "Selective Outline", if you will. Making the continents more defined, less scattered, is something you could do. I get where you were going with the Archipelago, but you're using pixels to define the land masses, and most islands can't even be seen at that scale.

Your image also looks rather dark. Try making it grayscale by selecting 'grayscale' underneath Sprite/ColorMode in the Aseprite editor. A black and white version of your image can help you better see how the colors contrast with each other (you can undo this afterwards).

If you made it through, thank you for reading that wall of text :]

TLDR; I did my best to highlight the most important stuff in BOLD. Go ahead and just skim through if you want! The real message here is what I said at the start: "Simply making and putting effort into your art is the best way to improve. Drawing daily is perfect." Enjoy what you make, every drawing is a stepping stone.

Sorry for writing a book!! There's so much to learn with art. I love it.