I keep a show book, kind of a cross between an account book, diary, address book. So for every show, I have a record of the weather, number of people who attended ( if the organizers don't announce, I ask ), new contact addresses, orders, costs and sales plus anything else that I might think of.
I have the world's worst memory so I write down everything. I have written down things like birds nests above ( avoid that tree in future), underwear that kept slipping ( very uncomfortable if you aren't in a position to hitch it up), closest Dollar stores, food vendors I like, food vendors that I don't..
When I get home the information goes into a file for that show. and I assess it. Sometimes the information points out something new. One venue that I have done for years does better if its raining. It rains a lot in that area and a bit of wet doesn't bother people but in good weather they stay away in droves. Talking to other people has found cheap gas places, less expensive lodging, better shoes, good shows. A lot of it is the same kind of information that we all share here.
The accounts for the shows are important and thats there too.
I have to work smarter to make up for some of the shortcomings my ageing body is throwing at me and the book really helps.