You'll find in this post all the resources and instructions available to make new parts and decorations for Mecabricks. It will be updated when new content will be added.

Decoration Workflow
Mostly current but needs to be updated to include bump maps and metal maps.
http://www.mecabricks.com/en/forum/topic/268
This thread can also be of interest http://www.mecabricks.com/en/forum/topic/128

Colour Chart
This table contains the hexadecimal values for all the materials available in Mecabricks as well as the conversion from other systems like LDD or Bricklink.
http://www.mecabricks.com/docs/colour_chart.pdf

wlange has also created swatch libraries for photoshop and illustrator: http://www.mediafire.com/file/tnfoui8jxkra6f7/Mecabricks+Colors.zip
UmbraManis did the same for gimp and inkscape: http://www.bricksafe.com/files/Umbra-Manis/OpenLDDFiles/Mecabricks.gpl

UV Maps
This folder contains all the UV maps available for Mecabricks. Please make sure that the decorations you create are of the same size as the corresponding uv map.
https://drive.google.com/open?id=0B3dmCtByvZwEZU5xY1d4Smg2ZGM
I also wrote a guide about uv maps for minifigure decorations https://www.mecabricks.com/en/forum/topic/1357

Icons
[Update] Icons are now automatically generated on the server without the need to use a third party software.

Drop Box
To submit you decorations, please use the Drop Box section of Mecabricks. Guidelines are also provided in this post.

Videos Tutorials
[youtube]4t46QwhQbJQ[/youtube]

[youtube]mwQwW0yCODg[/youtube]