SEO - Search Engine Optimization of Google Sites is not like the SEO of other websites platforms like WordPress, Joomla, Wix etc. There are many reasons beyond this, for example: we don't have the control on page HTML and can not work with the key tags of SEO like <meta> tag. This does not mean that you can't rank up your Google Sites website in search engines. You can optimize the Google Sites and do it very well. You need to understand some basic guideline about SEO of Google Sites.
SEO tips in Google Sites SEO guide are very useful if you read and apply them on your Google Sites website and you will get good ranking in organic search results.
Note: You can skip it and jump directly to Google Sites SEO guide if you have some understanding about SEO.