I also make a spreadsheet of my feed schedule to keep on track. I use a white board near my grow so I can make some notes on the fly and not forget about it later. I was keeping a ton of photos but it eats up too much real estate on my hard drive. Now I only document things that are unusual or unexpected.
Let me know if there are things I missed that you think are important to look back on.
This an example of a grow from last year: