There are many design techniques that can be used to build a website. These techniques are what we collectively refer to as web site structure. The 3 techniques that hinder SEO are frames, layers and dynamic pages.

Frames
A framed site is one where the page being viewed is actually a collection of pages pieced together. These are usually identified when you see a section of page remain still whilst you are scrolling.

SEO Problem
Search engines are unable to piece pages together to form a framed page. Therefore they are unable to fairly rank a web page that is in frames. Framed pages are at an enormous disadvantage with SEO and should be removed.

Layers
Layers allow designers enormous flexibility when placing information and graphics on a web page.

SEO Problem
Layers can be used to hide information. For this reason search engines heavily penalise web sites that contain layers.