I would start at SEOBook.com, but know this, it is not an easy field to break into. You will need to have some success on other websites before hanging out your shingle. There is a big rush to join
SEO/SEM without earning your stripes.
Most who have become success in
SEO did not set out to do so.
SEO was developed while running and managing other websites. You should first start out with a niche blog or two acquire your skills on your own websites before you consider asking to work on someone else's site.
There are lots of training available but you have to be able to apply this training and create a verifiable track history first. To see what's available do a Google search for "
SEO Training Courses."