Copying output from Mathematica can be tricky at times. Here are some tips on making it easier:
Copy As -> Plain Text, or
Copy As -> Input Text from the context menu to avoid copying (not really human readable) box expressions.
If you copy only input cells, the In/Out labels will not be copied. To select all input cells in a notebook, Alt-Click an input cell bracket. (You can copy the relevant section to a new notebook before selecting input cells.)
Whenever possible, make sure that the code posted can be copied back to Mathematica and evaluated. But in some special cases it's good to show the formatted expression too, as a screenshot. The image uploader palette makes this very easy.
Unfortunately formatting (indentation and newlines) will get lost when the code is copied. I do not know if there's a good solution for this (I'd be very interested!)
- When pasting back code to Mathematica, it'll get pasted into a single cell.
Cell ->Divide Cell (CTRL-SHIFT-D) is a convenient way to break it into parts again.
A note about In/Out labels:
When I post code to be copied as a whole, I always avoid In/Out labels, as this is inconvenient. But when I'm showing the process of doing something, together with the output, and commenting on each step, I prefer to keep In/Out labels to make it very clear what is the input and what is the output.