Motivation is the most important element when teaching anything, including English. Learning English when not motivated is one of the most difficult things in the world – but when motivated it turns into a pleasure with improvement and positive reinforcement.
One of the tricks for motivation is to focus on what your learners are interested in. Remember that even an English native speaker won’t want to stand up and talk about something they don’t know anything about. Ask your learners what their hobbies are, what they did at the weekend, what they like doing, what they think is interesting in the news, what their aspiractions are. Then react, either to individuals, or to topics that seem to get the class interacting, and develop your lessons around those ideas.
As all English tutors know, if you can get your learners speaking it will accelerate their learning. If you have a learner who is interested in cooking, they will be interested in learning the vocabulary, and then the verbs, and then the adjectives, and so on related at cooking. Bring in simple recipes, and perhaps even ask them to cook something to bring in with the receipt to engage the whole class. Similar if a learner is into rap, ask them to bring in a song, help them with the translation or understanding, and look at it with the class.
Don’t worry about moving away from the syllabus; if they are motivated they’ll be working at twice the speed and a higher level than when you left it!