For ripped sprites, you can find some guidelines here. You can also just look at many of the existing sheets.
For custom sprites, you can also look at the existing custom sheets, but I would suggest also posting them in the Custom Sprites/Pixel Art section for feedback from other members.
For custom sprites, you can also look at the existing custom sheets, but I would suggest also posting them in the Custom Sprites/Pixel Art section for feedback from other members.