Hi, Isabel.
It would be nice to put this post in English because I �m sure teachers no matter the country can help you, not just from Portugal...
First, don �t panic!It �s natural that you don �t kow your students at this stage but prepare them a placement test.
Before that you could hand them a questionnaire in which they can refer their previous knowledge in learning English Language, their preferences in teaching resources(handouts, fims, Internet).
In this questionnaireyou can also find out what they think about the importance of learning English in their personal and professional life, what are their expectations regarding the course.
Of course you can put the questionnaire in Portuguese if you sense they don �t have much knowledge yet...
Don �t forget to make a planning with your sts aims , contents , strategies and resources after having the questionnaires in your possession.
Hope this can help you!