If you are just starting out my best advice would be to buy a couple of trial and error domains, read the internets many archives of SEO information, come to your own conclusions by trial and error applying and experimenting with what you have found to those trial sites, don’t start on a serious business domain unless your sure of what you are doing or apply only minimal changes to anything serious, other than that get an expert. The subject is way too large to be listed in any thread but I believe there is some good bulleted lists out there i.e. 10 biggest mistakes etc. Here’s one: http://www.searchengineguide.com/1stsearchranking/2005/1103_1st1.html