I've written a simple spreadsheet that tracks date & source of enquiry, whether converted or not, value, type of jobs and date completed along with customer details.
Also then produces a monthly graph showing number of enquiries per source, conversion %, total income for each source per month and average job value per source. As the year progresses it keeps an annual running total of each of those. Thinking about breaking the numbers down by carpet, upholstery, hard floor etc.
Just copy and paste the graphs into the monthly business review / planning document so it is easily kept track of.
I keep it on google docs where it is hopefully nice and safe.