Its not exactly a dark art, its just very time consuming. Its taken my companies website about 18 months to get to Page Rank 3.... does well with my targeted search terms.
Best thing to do from my experience, is:
1- to research keyword popularity and competition
https://adwords.google.com/o/Target...&__u=1000000000&ideaRequestType=KEYWORD_IDEAS
2- Find keywords/terms which are not to heavily used but searched often by users
3- Ensure you have this term in your url... i.e
www.mywebsite.co.uk/big-guns-rule
4- Make sure you content is fresh with regular use of your targeted keywords. I generally try to use a different term focus on the different pages. Some people think that using bold on your keywords, H1, H2 tags etc... make a difference, I'm not to convinced by its best to try different things to see your results.
5- Then the hard/PITA part, get as many quality inbound links as you can. Relevant to your content, and with the highest PR possible. Use directory submissions, blogs etc etc...
Takes a lot of time, but I haven't touched my site for around 12 months since the initial SEO push and it has gradually gotten a higher PR over the period.
Oh, a great tool to see check out your sites performance, and the competitions is...
http://www.opensiteexplorer.org/ - also use Yahoo/Bing tool -
http://www.bing.com/toolbox/webmaster & Google Webmaster
Hope that helps.