In order to successfully promote your site, you first need to check whether it really is a CEO friendly. SEO promotion will depend on the structure of your site, content, and convenience for visitors. It's also very important to have a mobile version of the site. I know that for websites created on Magento there are many extensions and applications that affect SEO promotion, here
https://www.mageworx.com/ you can read more about some of them. It seems to me that you shouldn't spend money on SEO promotion if your site is not SEO friendly, it will not help you promote your website.