In John Mayer's style.

How to achieve the solo style of John Mayer?

A mix of major and minor scales really translated into blues is a good start at achieving JM's sound. 

When soloing think of the scale you are in by deciphering the key center. 

First of all, get to know your key and count a 6th above. That will give you the minor key center. That minor key center will become the Tonic for the blues scale you will need. 

Example:  if the song is in G major, then the 6th degree will be E, and that will be your blues center point. So, play on E blues. 

Mix this blues scale with passing tones of the major scale it bongs to, and you will come very close to having the tools necessary to play a solo in the style of John Mayer. 

Although a very simple concept, it can be challenging and interesting enough when used effectively!