I'm no expert on ponies, and I don't have the book to hand right now (will edit if I remembered it wrong) but here's some pretty standard, pretty universal guidance adapted from the excellent Lessons in Classical Drawing by Juliette Aristides plus a few tips from Draw by Seeing
- The important thing to understand is, there's an internal conflict between the actual nuts and bolts of how the drawing should look, and what you understand about the meaning of the drawing. You want to start with the eyes because they're the most interesting, engaging part. But starting there won't help compose the drawing and could cause the overall drawing to have wonky proportions. You're not thinking about the skeleton because, who looks at a pony and thinks about the skeleton? But it's central to structuring the drawing - the skeleton's posture and position drives everything else.
- Find some reference image, or, get the clearest possible mental image in your head. Start by roughly sketching out the overall shape. No detail, no shading yet. Big fat light grey blob brush. You're marking out the space you'll use and the space you'll allow yourself for each element. (digital tip: find a drawing app with layers, so you can turn these guides off and on freely)
- If it's anatomical, whether to use a skeleton depends on how accurate you want it to be - but it's generally a good idea. It reduces the chances of the pose, positioning, relative sizing and composition looking wrong later on. At the very least, I'd recommend thin lines for the spine, legs, neck etc and a few ovals for the head. (separate layer to the blob outline, you'll probably find yourself changing the outline based on the skeleton and vica versa).
- Then work through from the broadest detail to the finest. Outline of the overall shape, then give it volume with basic shading and highlights, then all major details, then all fine details. It goes against instinct (you want to dive straight into the interesting engaging bits like eyes and face) but it helps avoid trapping yourself in a with an excellent detailed face that just doesn't fit the rest of the drawing, and it helps you appreciate the right level of detail. If it's going well, you should get some sense of the character of the thing you're drawing at each stage, even before it has big cute eyes.
There's not one "right" method, these stages are meant as a rough guideline and can be modified and re-ordered to suit style, but, there are universal principles driving this: in particular, the importance of getting a handle on the overall shape before diving in to the interesting details, and of looking at it at different levels of detail.
And drawing is as much about observation as it is creativity and hand-eye co-ordination. And observation involves the difficult art of seeing how things actually are, seeing through than how we humans interpret them or think they 'should' look. Even if you're drawing cartoony caricature things from imagination, it should be lead and informed by actual observation. Disney animators spend ages observing and studying the anatomy and motion of actual animals and people. There's a highly rated book I saw recommended somewhere about how to draw imaginary and highly stylised things in a way that looks 'realistic'... can't remember the name, but observation was a key theme.
Re. the question about lines looking mechanical - depends on what style you're going for. If you can, using a pressure-sensitive pen tablet (e.g. Wacom Bamboo) will make you able to make more different styles work.