The answer to this one is going to vary wildly. It depends on you and the company you work for. The company will dictate how ,many people come through the door for a trial lesson. It will depend on you to get those people who want to get a ppl to learn to fly with you. A newby instructor will earn less than an established instructor - fewer clients.
I worked in the south east for a biggish company and earned about £17k pa gross in my first 2 years instructing, but there are people out there earning a bit more. That was based on about 400 hours a year, working full time. WE did get paid a nominal amount for ground school.