Search engine possible seo problems

Hi guys

My first site will be a search engine site written in html, css and mysql,php for the search part.

As Im just learning the mysql,php part are there any seo issues that I should bear in mind whilst writing it..?

Ive pretty much covered the content, tags etc etc for the main build but just wondering about the php side of things

What kind of search engine are you writing? One that plays off other SE's indexes or are you actually indexing yourself?

indexing my own content