I've only gotten back into skinning recently, so I'm probably not the best person to listen to, but here's some general stuff that's helped me:
- Try drawing out how you want the character to look on paper first. That way you're not just sitting in the editor with only vague ideas for what you want things to look like.
- Usually, I like to lay down my base colors and shapes before adding any shading or detail, just to work out where everything is.
- TEST YOUR SKIN IN-GAME AS EARLY AS YOU CAN. I can't tell you how many time's I've had to re-do sleeves because I put what was supposed to be on the outside on the inside. The earlier you try to correct a mistake, the easier it is to fix. The new launcher has a cool thing where you can view your skin without having to run the game, which is great for saving time.
- Make different parts as distinct as possible. You want to be able to tell what's hair, what's a shirt, etc.
- Don't use neons! One super-bright color is ~maybe~ okay for accents, but any more and the skin hurts to look at! Bright colors are still great, just tone it down a little bit. I know it'll look dull in the color picker, but please try to use less-saturated colors.
- Don't shade with a darker version of your base color. Shift it slightly in the direction of a different color. For example, when I'm shading red, I might make the shadows a bit more purple and the highlights a bit more orange.
- Use an editor that lets you use transparent brushes. Not only can you make transparent pixels on the second layer, but it makes shading a million time easier.
- There are many different ways to do eyes, hair, scales, etc. Experiment with different things! Play around and find a style you like!
- Use the second layer to add more shapes to a skin. Alternatively, if you can't figure out any way to add shape to a body part, use it to add a customization feature (I'll use this to add removable wings sometimes! Keep in mind that this will make your skin look a bit flat and blocky, but hey, it's minecraft).
- Finally, have fun and take breaks often! Also, don't take anything I'm saying as a hard rule. It's all just suggestions.
That's about all I've got. Good luck :D
