Negative prompts tell Stable Diffusion what to avoid — one of SD's most powerful features and absent from most other image AI tools.

Standard Negative Prompt (Use as Default)

ugly, deformed, noisy, blurry, distorted, out of focus, bad anatomy, extra limbs, poorly drawn hands, poorly drawn face, mutation, mutated, worst quality, low quality, jpeg artifacts, watermark, signature

Anatomy-Specific Negatives

extra fingers, missing fingers, fused fingers, too many limbs, bad proportions, deformed hands

How Weight Works in Negatives

Use parentheses to increase weight: (deformed:1.3) means 1.3x stronger avoidance. Double parentheses ((ugly)) also increases emphasis.

Reference:

Negative prompts guide

https://en.wikipedia.org/wiki/Special:Search?search=Negative%20Prompts