When using a word processor or creating electronic documents, we become typographers. 

According to sources, there are no rules, right and wrong do not exist. There is only effective and non-effective communication. Modern word processors allow for flexibility.
 

"All those rules we are supposed to follow were developed 20-400 years ago. They were developed at a time when people had not even dreamt about cable-TV, interactive media, CD-ROM, Internet and graphic applications. Human beings were not stupider than today. However, media have dramatically changed. When media change, men change." (http://desktoppub.about.com/gi/dynamic/offsite.htm?zi=1/XJ&sdn=desktoppub&cdn=compute&tm=30&gps=188_371_1003_611&f=00&su=p284.9.336.ip_p504.1.336.ip_&tt=2&bt=0&bts=0&st=31&zu=http%3A//www.typ.nl/TYP04/woud/illegibility/illegibility02.html)

 

To communicate effectively, we arrange text and graphics on a page and produce a document for printing. Four general areas apply: (http://desktoppub.about.com/cs/basic/a/textcomposition.htm)

• Placement / Alignment
• Style (Size, contrast, emphasis)
• Spacing
• Embellishment / fine-tuning

It is all about readibility, legibility and effective communication and consistency.
 

Common mistakes:

1. Using underlined text to emphasise - rather use bold or italic
2. Using two spaces after a full stop, comma or paranthesis - these should be followed by one space, not two
3. Using keyboard quotes - rather use straight quotes
4. Using all capitals for headings - rather use styles and/or different font sizes, etc.