As your students are all adults, you could think of making a small survey in class to see what they are the most interested in. Museums are, in my opinion, a great idea of a place to visit for an English day trip. If you look around and get some information on the different museums you have close to your school, you can probably find one which provides an interactive visit between the guide and the students so they can both learn and talk in English. This can test their comprehension and make them entertained as well. I am pretty sure you can find a topic which interests the majority of your students. As for the procedures you should think of, samuel quite covered most of them. I hope this helps you!