If you don’t have a mobile-friendly website, start there.
A mobile-friendly website adjusts to the screen size of the device that views it.
All online traffic used to come from large computer monitors. Now, most traffic comes from smartphones and tablets. If your website doesn't respond to screen size, you are frustrating potential customers and losing business.
On top of that, in 2015 Google made mobile-friendliness a ranking signal. Mobile-friendly sites now rank higher than non-responsive sites in Google search results.