Try not to use too contrasting colors (ex. Neon green and neon purple in the same skin and/or area of the skin, unless it's the specific theme of the skin)
Don't make the shading too light so that you have to look really closely or move your head to see it
Don't put too many colors in one skin, especially on the same body part
If you're lacking inspiration, look at the popular skins on here, skindex, and namemc. Or even search up minecraft skins on pinterest and look at the ideas there :>
That's all i got rn
