https://anthonyhobday.com/sideprojects/saferules/

Here are some visual design rules you can learn once and use many times in your career. They’re safe.

Don’t use pure black or white, only near-black and near-white

Pure black looks unnatural on a screen, and pure white is too bright. Use a vey dark and very light grey, respectively. Any other references to “black” and “white” in these rules assume you’re following this rule.

Saturate your neutrals

A neutral is generally a black, white, or grey. If you use colour in your interface, add a little bit of that colour to your neutrals. If you use the HSB colour system (and you should) less than 5 Saturation should do it.

Use high contrast for important elements

Important elements means buttons, content, or anything else that the user needs to notice. Elements that the user does not need to notice (e.g. structural elements, drop-shadows) can use as little contrast as possible.

Everything in your design should be deliberate

This is vague, but important. You should be deliberate about absolutely everything in your design. This means whitespace, alignment, size, spacing, colour, shadows. Everything. If I point at a random part of your design and you don't have an explanation for why it looks that way, you’re not finished.

Optical alignment is often better than mathematical alignment

Mathematical alignment is when you tell your design software to centre something in its container and think you’re done. But some shapes don’t suit being aligned in this way. Very often you will need to align things by eye so that it looks good.

Lower letter spacing and line height with larger text. Raise them with smaller text

This applies to all text. The bigger the text, the less space you need between each letter and each line. The reverse is also true.