I suggest you search for sprite sets on the internet. These are just like graphical DF tilesets that other games use. Look for ones that have a very limited palette.
Pixel art is all about a limited palette, ideally you should be able to work in a .png file. I suggest just using MS Paint, but you can use whatever. You honestly don't really need much.
Start out with something fairly simple. Try making something Final Fantasy or Zelda: link to the Past like, from the front but slightly above. Just try to draw stuff. Like a sword or something. I suggest a larger image, 32x32 would be okay. 16x16 is pretty limited but you'd be surprised what you can get away with.
So say you're trying to make a dead fish - like something the fisherman caught. Start with a work space that has white area around it and a grid of 3x3 boxes of the size you want. Use a weird color like magenta for the boxes so you won't get them mixed up.
It should probably be blue. So go into the color picker and grab a blue that you like for the overall color. Draw a little square of it somewhere, say 10x10 pixels. Then pick a shade 20 Luminosity brighter and draw a square of it above your medium blue. Then pick one 20 luminosity below your medium and stick it under. You can expand your palette outwards if you want, 5 shades of a regular blue is usually pretty good. If you wanted a blue-green, you'd pick out five shades of that. A medium red = a new palette. So you might end up with several mini palettes like this.
Draw your fish with the pencil tool. Just an outline. Refine it to get the outside shape right. Try to make it look plump. X for an eye! Make sure the finds aren't too big. And your outside line should be one pixel wide.
If you have a bend, don't draw up one pixel and then over one. Just use a diagonal. Otherwise when you zoom out it looks blocky.
Paintbucket into the fish with your medium blue. For the fins and head, use one color lighter as your medium. You probably don't need a line to draw the shape of the head but you should for the fins. Where the side fin meets the body, don't draw the black outline. That suggests that it blends in. But you might feel like the head needs to be outlined where it meets the body.
Now that your fish body is medium blue and your fins and head are medium +1, start shading. Determine where the light comes from. Remember that your fish is plump - you get most of that effect from the shading. On the areas lit by more light, paint +1 palette. In the areas that are under the fish, in shadow, paint -1 palette.
If your fish is tail to the SW and head to the NE, then the underside fin will be darker than the top fin.
Now you may feel like you want scales. I suggest not drawing scales with the black outline. Instead, anywhere you want scales, draw dots in a pattern that are -1 brightness for that area. I suggest leaving the head smooth. Straight lines like this from the body outward on the fins suggest the finny spiney shape.
Remember a little mouth! Experiment with different mouth shapes. It'll just be 4 or 5 pixels on a 32x32 but a shift of one of those black pixels will make a huge difference.
You'll find overall that you'll be fiddling with one pixel at a time a lot. As you advance you'll expand your palette slightly and use more bands of shading. Maybe even dithering.
You won't be using the spray paint tool. It just looks ugly. Pixel art isn't about noise, it's about careful placement.