- Large icons should cover at most 22x22px. Always leave at least 1px empty on each side.
- Align to a 1px-grid whenever possible. (Make sure the grid [#] and snapping [%] is on in Inkscape.)
- NEVER use the same symbol to mean two different things. Never use an icon from another icon set to mean something different than it means in that icon set.
- Put tango icons under the "tango" layer.
- Except for the "save" symbol, always use symbols from https://github.com/GNOME/adwaita-icon-theme rather than custom ones.
- Design icons to have the same style as the full-color Gnome icons.
- Other than that, refer to the Tango icon guidelines: http://tango.freedesktop.org/Tango_Icon_Theme_Guidelines .
- Put symbolic icons under the "symbolic" layer.
- Except for the "save" symbol, always use symbols from https://github.com/GNOME/adwaita-icon-theme rather than custom ones.
- Except for color-dependent metaphors, use the same metaphors as the Tango theme uses.
- Use only the color #555753 (RGB 85-87-83) at either 100% or 35% opacity.
- 16x16px icons use 1px thick lines, no need to leave 1px empty on each side.
- 24x24px icons use 2px thick lines, always leave at leasr 1px empty on each side.
- 32x32px icons use 2px thick lines, always leave at leasr 1px empty on each side.