tedster - 2:51 pm on Sep 7, 2010 (gmt 0)

I'm increasingly finding that SEO is very much trial and error

And it always was - it's just that there is an accumulated body of discoveries that are sometimes taken as "the gospel". But things change and there is no gospel. There is only vigilance: new trials to confirm what we think we know, or to explore what we might learn.

could someone explain 'html markup' please

HTML is an acronym that stands for Hypertext Mark-up Language.

There is a key concept here that took several years to fully sink in for me. But you can bet that it's the key underpinning for any search engine's approach.

First there is a document of some kind. Then various parts of the document are "marked up" with tags that add information about how those parts relate to the whole.

HTML is not a layout application - it's a way of adding semantic structure to raw information. In other words "content is king" - or maybe "content is the grandfather".