Here's the spreadsheet I ended up making with the feedback I got. I left a couple example trades in there.
Making trades is probably my favorite part of fantasy baseball. By default I (and probably all fantasy players) assume that I win most trades I make. But I have pretty selective memory and it's easy to forget the mistakes. So with the spreadsheet I was trying to figure out if I should be more hesitant to pull the trigger.
I searched back through my email history to get all the trades I made in the last couple years ("team name" and "trade processed" or "trade agreed"). Gmail listed them out nicely for me so it didn't take very long.
Because its hard to define a trade because of context, etc, I decided to just record "would I make the trade again?".
And generally the trades I'm making are working so I'll carry on.