I think using synonyms and antonyms is a very effective way to expand new vocabulary. It involves students' existing knowledge and also challenge them to expand it. Learning synonyms can help students to avoid repetition in their writing, achieving more complexity of vocabulary, too.
When we are learning a new text, can have student self-select the words that they do not know and make a list of them. Then the teacher can list them on the board and have the whole class find their synonyms together. Or, students can work together as groups to do synonym or antonym practice with the help of dictionary.
Besides, visual aids are always helpful for beginning learners, both younger learners and adult learners. I know a lot of Chinese students use an application called "100 words to kill one day" to prepare for TOEFL and GRE tests, which combined vocabulary, pictures, pronunciation, contexts. It is a very helpful tool.
If computers are available for students in class, flash card tests like Quizlet will be very interesting for students. When there is a timer, students will get excited when they are doing the tests. However, it might not be helpful for students who do not have this technology in their classroom.