Check Format|Paragraph and space after. If there is 6pt of space set here
that would account for the space after a return is pressed.

Thanks for the reply.  Have checked like you told me - Before is set for 12
pts and After 0 pts.  Any other suggestions?

You want to be using different styles for different parts of your document.
http://addbalance.com/usersguide/styles.htm and
http://www.shaunakelly.com/word/styles/TipsOnStyles.html
The spacing you are talking about is space before or space after paragraph
formatting. Each time you press Enter, it starts a new paragraph.

You can set up one style for the first address line, usually the name of a
person. That might have 36pt spacing before. Have an address line style for
the rest of the address, it has no spacing before. Set your first address
line style so that it is followed automatically by the address line style.
Use macrobutton fields to create click-and-type areas to insert information.
These can be preformatted. See
http://www.addbalance.com/usersguide/fields.htm#MacroButton,
http://www.gmayor.com/Macrobutton.htm and
http://www.mvps.org/word/FAQs/TblsFldsFms/UsingMacroButton.htm for more
about macrobutton fields.

When I talk about setting this up, I don't mean each time you sit down to
type an invoice. You create a template and use that as the basis for new
documents. For more on the different kinds of templates, tabs on the file
new dialog, and locations of templates folders see
http://addbalance.com/usersguide/templates.htm.

If you are going to be using Word much at all, you really need to spend the
time to learn and understand templates and styles. Otherwise, you'll be
beating your head against the wall every time you sit down at your keyboard
with Word. If you aren't going to be using it enough to justify this
investment in learning, I would suggest using WordPad instead; you'll have a
lot less frustration.