Since the release of Factorio 0.15 this is simple: While creating a blueprint you have the option to export it as a string. This is the string you can share with the community. For already existing blueprints AND blueprint books you can simply open it (like you would open a assembling machine) and find the export button there.
This is the button you are looking for (here in a blueprint book):
The result will look like this:
When creating your post here in the forums the text editor should contain something like this (this is what generates the above example):
Code: Select all
[bp]== replace this with your blueprint-string ==[/bp]