The SEOmoz
beginner's guide to SEO would be a good start. Reccomend printing out the MS word version and digesting slowley over a week or so.
There are no tricks, it's just a long slow slog that can take months or even years to come to fruition.
Anyway,
Make sure your pages have a logical structure.
Use text instead of images where possible.
Make sure each page has unique titles, descriptions, headers and content.
Write interesting and informative articles.
Keep adding new content.
Use social networking and community sites to made yourself known as an expert in your field.
Be different to everybody else.
Be patient.
Forget link building for now, just make sure the site is the best it can be - that doesn't mean perfect, just as good as you can make it without agonising over every comma and full stop.
On the other hand, if you have a site that is similar to thousands of others then you are going to struggle to even get noticed let alone increase your visitor numbers.
How are the businesses going to advertize? PPC banners or skyscrapers or box adverts or what? Click through rates on adverts are usually tiny, well under 1%. So if you are getting a penny per click with a click rate of 1% you are going to need 10 000 visitors to make £1. Is it really worth the effort?