austtr - 1:11 am on Jul 15, 2011 (gmt 0)
The three elements together should give an accurate reflection of the real purpose of the page.
A common mistake I see (IMO) is pages with title tags crammed with search terms applicable to the whole SITE. The title tag and description snippet need to accurately indicate the purpose of the PAGE.
Titles and descriptions are first and foremost about telling the searcher what to expect when they open that page. By all means optimise the tags for key words but keep it relevant to the page.
This is all very elemental stuff, but in light of the OP, it might be worthwhile revisiting some of the "on page factor" basics.