For best optimisation of social media I would suggest that a business builds a website for digital presence. Let’s face it if you are not visible on the internet it makes it hard for customers to trust your brand

SMM benefits businesses in a variety of ways, the most important of which is establishing a dialogue with customers. Social media enables customers or consumers to communicate directly with brands forever changing the way organisations operate.

It depends on the type of brand/ company.

If the goal is conversation, track content downloads, online sales, webinar registration etc. But if the goal is engagement, learn how many people participate, comments, replies or shares