For my part I tend to write documentation as I write code :
I wrote a general (abstract) documentation, then I add more detailed parts.
(then I iterate the second phase until satisfied).

Note that you can do it

• In the same document
  Taking care to put the simple abstract part at the beginning and hiding as much as possible the too specifics details (in an APPENDIX for example)
• In several documents
  This allow you to specialize your documentation to the reader
  (Beccause a techie don't need the same informations as a commercial...)

The second way is my favourite way, I usually make a (very) small doc describing the product
(just to make the reader understand what we're talking about)
I then write a more detailed document with links to several other (specialized) docs (Appendix, user guide, maintenance guide, sysadmin's guide, developper's guide...).
document.

Last note: 'the quick install' and 'common troubleshooting' parts seems to me the most used part of a technical docs
(at least at my office), it may be worthy to write them with a special care...

UPDATE : The 'links/resources' part is also a must write to my mind...

UPDATE 2: As I realize that my answer may be far from practical, I'll add some common useful guidelines :

• Write a READABLE way
  Otherwise nobody will (be able to) use it...
• Adapt your text to your reader (the content AND the form)
• Don't forget your initial goal
  your technical doc shouldn't become a technical rant about how good the solution is...In the same vein in a commercial documentation, it's totally useless to explain your over-smart technical hack, speak about technological advance ;-)
• Use spell checkers (It's VERY important for some people (usually your bosses ;-))
• Use a portable format to allow other people to work on your documentation, convert it...

"Only Bad Coders Code Badly In Perl" (OBC2BIP)

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.