Index -> Navigation -> Preferences -> Quick-Join Prefs.

Quick-Join Prefs.

This area lets you specify what sort of games you want to be considered when you click the Quick Join button at the top of most lobby screens. Preferences are set separately in each lobby. To set your preferences, right-click (ctrl-click for Macintosh users) the Quick Join button, or to join the first game that matches your preferences, left-click the Quick Join button.

For example, if you wanted to only join two-player Standard format games with people on your Buddy List, select Standard from the Play Format menu, click the Buddy List Only box, select Two from the Number of Players menu, and select Save. The next time you click on the Quick Join button in this lobby, you will only join games that conform to these criteria.