Your digital marketing strategy should focus primarily on what is called 'Conversion Rate'.  It is easily calculated as the number of sales or signups or clicks divided by the total number of visitors to your website or your email campaign, multiplied by 100!  Thus conversion rate is a simple calculation.  

Suppose your website was visited by say 200 people on a particular day, 6 have made purchases of your product, then the conversion rate would be 6/200 X 100 = 3%

Conversion rate is a very crucial metric in the sense that it paves the way for your improved relationship with your customers and the enhancement of brand awareness.  Conversion rate is aimed at to build an increased flow of revenue into your business.