How to work out industry average?

Hi guys,
This is my first post. I have very little knowledge of statistics. So please correct me if I am wrong.

I have data for past few years for some local businesses from the same industry. I know how to work out the sales trend for single business but how should I go on about working out the average sales trend for the whole industry? (So I can compare the individual company's trend with industry's trend and explain how well he is performing).

I was thinking of taking the sales for each quarters for all businesses, average it and then process time series analysis. E.g. Business a Quarter 1 (Q1) £200, Business B Q1 £20, Business Q1 £500. (200+20+500)/3=£240 average for Q1 for the industry. Q2 £300, Q3 £100, etc.

Is there any other methods I can use? Can you please refer to any website or book or any academic theory so I can do further research. Thank you.