Who's your target?
I think an important thing to get your head round before you start, is who / what you are optimising your pages for? (Getting orders, pushing your company brand etc...) I got this search splitting idea from a video I watched, and think it's a good easy way to look at things.

If you split the way people use search engines into 3 Kinds of searches:

Navigational:
People trying to get to a site or company they know

Informational:
Getting information on a specific subject / Researching

Transactional:
People wanting to purchase products... Might type specific things into SE's i.e. "Unlocked Nokia N73 New York" or variations of etc..

You need to think about how you would optimise your pages for each specific searcher, for example the further you drill into an ecommerce site to a product page - You would want transactional surfers to be targeted, so you might (Notice I said might, as above I am only giving examples I am not saying this is the right or wrong way) use the following Page title and optimise the page accordingly

"Cheap Nokia N73 Mobile Phone | Unlocked | Free Delivery in New York"

Location:
This is another good thing to bear in mind when drilling down the search chain... Instead of trying to optimise a page for say "Cheap Hotels" which a million other websites are trying to rank for (And have HUGE SEO budgets), try going for a more specific market "Cheap Hotels in Harlow, New York City" or some derivative or be even more precise if you can... Use the Overture tool below to find interesting new key phrases

Layout:
I have listed a few sites below in regards to people's eye movements when browsing a website - Its interesting to see where the most prominent areas of a site are, and I suggest you give them a quick once over.

A Few Cool Tools:
1.) Overture Keyword Suggestion Tool
2.) Yahoo View Bids Tool
3.) SEO Book Tools
4.) GSiteCrawler
5.) 301 Header Checker

Research / Websites:
1.) http://www.cre8asiteforums.com/forums/
2.) http://www.highrankings.com/forum/
3.) http://www.mattcutts.com/blog/
4.) http://www.webmarketingplus.co.uk/index.html
5.) http://www.enquiro.com/research.asp
6.) http://www.poynterextra.org/eyetrack2004/main.htm

In-bred Search Engines:
I think this might be a bit out of date now, but this is a really cool thing to see how all the search engines and directories are connected and what relationships they have:

http://www.bruceclay.com/searchenginerelationshipchart.htm

Well that's my tips / suggestions whatever you want to call them - Please take them as you will and I hope they might help someone