While this was my second game jam, it's the first one where I did any amount of programming. In my other one, I only made music for a couple of games, but I did everything myself this time, so I was able to learn a lot.
For starters, getting people to play test the game before submission day is a good idea. I wasn't sure how to balance the difficulty of my game at all. I knew I was biased because I'm the one who made the game, but I didn't know exactly how much to offset the difficulty because of that. A number of people said my game was hard - and that was the entire point, I didn't want it to be easy - but I don't know just how hard is TOO hard, you know?
Second, I learned that there's nothing wrong with changing your idea. I had basically completed the game about halfway into the jam, but then I realized that I didn't have a connection to the theme at all. I brainstormed for a while and decided to drastically change the gameplay in order to be more fun, and have a connection to the theme. It was stressful, and I didn't get time to polish much as a result (I had to redo most of the code from square one) but it was worth it. I feel more proud of what I put on display than what I had initially made.
I also learned that there's no room for perfectionism sometimes. I tend to get bogged down by this a lot - I often don't even start projects when I have an idea because I am so deeply caught up in every single detail when I'm conceptualizing, but with this jam, I learned that sometimes, it's more about getting something on paper and figuring out the details later. You don't have to polish every piece of the system before putting it to work.
Finally, I learned that I am my own worst critic. This is something I already knew, and it's always proven true, but this served as a nice reminder. I was convinced that my game was utter garbage, and not worth playing. Totally thought mine would be the worst game submitted by a mile. But apparently, people actually enjoyed my game, and I'm really proud of that! It makes me feel a lot more confident in my abilities moving forward. I know my submission has a number of problems and it's far from perfect, but for once, I feel like I can make something that people would enjoy playing, and that's a super motivating thing to feel.