No one uses full sentences anymore (an unfortunate truth), because language is not all about grammar and structure, it is used for communication. However, you are not trying only to communicate, you are working on your language. The best way to do that is to use full and long English sentences. It will appear bizarre to people, but you can explain you are working on your English. Saying “Yes” and “No” is too easy, it’s level 1. You want to reach level 10, so you have to put in the work to get there. Using full sentences will get you there faster. I always encourage my students to fill the air with beautiful English. A good exercise: try using a connector (and, or, but, so, because) in every sentence. It will force you to construct two full sentences every time you speak. The more you flex your English muscle, the easier it will be to speak fluently when the situation requires it. Now go fill the air will beautiful English!