First of all be warned about rouge "SEO Specialists" who want to charge you an arm and a leg to optimise your website on an ongoing monthly basis. If one of these experts guarantees you a page one ranking, put your running shoes on and get out of there.
No one can guarantee you top results purely due to the reason that nobody knows the secret to the Google algorithm besides the Google guys (the owners), this is probably the best kept secret on the internet. The bulk of SEO is purely speculation and trial and error, nothing is ever guaranteed although we do have an impressive success rate using ethical methods.
In our experience the core of optimising a website is in the way a website is developed along with strategic keyword placement. By developing website layouts using CSS we eliminate a substantial amount of HTML coding, thus making the website easier for the search bots to index. The easier each page is to index, the more search engine friendly they become.