I will second Quassy's "Use common sense, mind your audience". The audience for elementary OS is overwhelmingly users who are coming from Windows and OS X. Don't confuse experience with intelligence. Knowing how to use Terminal doesn't make you any smarter than anyone else. Assume the reader is smart, but inexperienced. Remember this is a Q&A site. The reader is here because they are lost/confused and need help.
Please be very careful not to train new users to blindly copy and past Terminal commands. If you include a Terminal command as part of your directions, explain what the command does.
Remember that there is a very negative stigma about having to use Terminal. Reinforcing that stereotype is a negative reflection on the usability of elementary OS. Especially when Terminal is not actually needed to complete the task.
If it can be done without Terminal, I'd recommend giving directions without Terminal. Terminal is scary for a lot of people and at its core it is a developer tool. Kind of a silly example, but if someone asks how to rename a file, I don't think an appropriate answer is "Open up Terminal and type
mv...". Just give the easy answer (hint: it doesn't involved Terminal).