The most important thing what i feel is your codes you are going to code for your websites,thats gonna be the most important for seo ,other things such as title ,meta tags,header,footer.etc should be in such a way that your content get's crawled as soon as possible you add into your websites.Add site map to get the best outcome.use proper tags for headers,images.You can get w3c certification by checking/validating your websites code for the best results.