Honestly, teaching English to adults is very like teaching it to children. The only real difference is that most children are learning it while they're also still trying to get a handle on their native tongue, if English isn't their native tongue that is. So, you're able to actually communicate your ideas and issues with your tutee, and best of all, you can draw upon their knowledge of books and films. One of the tricks I used when I was helping my non-native English speaking friends to improve their language skills was to assign them reading which would entail reading books they had already read in their own language. So for example, Lord of the Rings was the one we used most often, as it was the easiest to come across, and the one which most of them had already read. They knew the plot from having read it before in their own language, so if they ever got really stuck they could worry the meaning out by thinking, "Okay, I'm at the Mines of Moria. What should be happening about now, and how does this help me understand this word in that context?"