Domain Age and Expiration Date
Google and other search engines include many factors within their ranking system. One of these factors is trust rank. Owning a domain that has history improves the trust rank as does registering the domain for a long period of time.
Again trust rank comes into play here. If your website has been archived in the search engine results for a long period then it will help improve rankings and indexing of webpages created in comparison with a fairly new website with no history.
When creating a website, it is important to provide a well structured navigation, not just for users but also to allow search engine bots to follow links and index webpages within your website. Structuring your navigation correctly can help all you webpages be indexed and should help the flow of Google's PageRank spread through out the website.
As with structured navigation, the importance of valid HTML to search engine bots is to allow all webpages within your website to be indexed within the search engine listings. Validating your HTML will ensure that the bots do not hit any 'brick walls' within the code that prevent them from reading the rest of the webpage.
To further help the indexing of your webpages and to even out the flow of Google's PageRank, it is useful to include links within the content text of your webpages. Wikipedia is a perfect example of how this should be done.
URL Structure Including keywords in your website's URLs will help you rank for those terms. If your website uses dynamic URLs created through variables then think about rewriting them. Separate keywords using a minus character (eg. search-phrase.html) and try and keep the important keywords as close to the beginning of the URL as possible.
If you wish to target a certain region then there are a few steps you can take to help this process. Firstly you can choose a relevant domain such as a .co.uk (UK) or .de (Germany) rather than a generic .com domain. Then look at your hosting IP location, search engines can access this information and will use it to decide your target audience. Finally, Google Webmaster Tools allows you to set a geographic target which is useful if you have a .com domain.
Search engine bots look for site maps when they visit your website. Providing a standard HTML site map will help improve the indexing of your webpages and allow bots to find webpages that they might otherwise have missed. You can now also provide and submit an XML site map which all the major search engines have took on as a standard. Use your robots.txt to tell bots where to find your XML site map and also submit it to Google Webmaster Tools and Yahoo Site Explorer.
If you are purchasing a domain name for a new website then think about including your main targeted keywords within that domain name. For example if you are building an online store that sells low price golf clubs in the UK and you buy the domain cheapgolfclubs.co.uk then you are definitely going to have a lot more of a chance for quickly ranking well for the search term 'cheap golf clubs' in UK search engines than you would with a more generic domain name. You would also do well for long tail search terms such as 'cheap golf clubs in the UK' and have more chance of ranking for 'golf clubs' in the long term.