This may seem a bit obvious but there is a different mindset you need to take into playing other games. When a designer plays other games, they need to be thinking about what works, what doesn’t work and pay attention to the other players are the table. A designer should be asking themselves (and make mental notes of the answers) while they are playing games. A few examples: How does the theme work with the mechanics? What parts of the games do other gamers enjoy the most? What kind of games make it to the table most often? These are just a few examples of the questions you should be asking yourself when you are playing games.
In addition to making various observations, you should be playing games to gain exposure to as many different themes and mechanics as possible. If you play a game that includes a mechanic you are thinking about using, pay attention to have the mechanic works and when it isn’t your turn, apply your theme to the mechanic. Use this opportunity to see how the mechanic moves pieces around the board or how the players interact with that mechanic. Playing games with other gamers is a as much an opportunity to learn about design as it is to have fun. The chance to see mechanics and themes used in way you never thought of before, and if gamers even like those themes or mechanics will go a long way to making your designs more successful and make your games more fun.
As an example, my Wednesday night game group has anywhere from 12-25 people show up every week. We have the same routine of starting the night with a game that supports a large number of people. The problem we run into it that we only have games that support up to 1o or 12 people. Normally, this is enough because most groups are not as lucky to have such a large regular showing every week. However, we have to split the group into two large games and while that works for us, I always feel like we are missing an opportunity to have a game with everyone in the game. Because of this, we have been working on a game that can support as many people as there are at the party.
Gaming with others is a great opportunity and designers should take advantage of these opportunities as much as possible.