I am a native Portuguese (European) speaker, an elementary school teacher, and I would like to learn English. Can you help me ?

Hello everyone ! I am a native Portuguese (European) speaker, and I am currently researching the best ways to learn English as an adult. I would like to be able to communicate fluently and understand native speakers. I am elementary school teacher and I would like to teach English to my students, when the time comes, but I have to improve my English knowledge beforehand. I have already learned some English throughout my life, but I still make some grammar mistakes and I still have difficulties in understanding native speakers sometimes. What is the most recommended course for my case? Thank you very much in advance.